Polypeptides and antibodies derived from chronic lymphocytic leukemia cells and uses thereof

ABSTRACT

Cancer treatments use a therapy that: 1) interferes with the interaction between CD200 and its receptor to block immune suppression thereby promoting eradication of the cancer cells; and 2) directly kills the cancer cells either by complement-mediated or antibody-dependent cellular cytotoxicity or by targeting cells using a fusion molecule that includes a CD200-targeting portion. The therapy includes the administration of novel antibodies, functional fragments thereof or fusion molecules containing portions thereof.

RELATED APPLICATIONS

This application is a continuation in part of U.S. application Ser. No.10/894,672 filed Jul. 20, 2004 which is a continuation in part of U.S.application Ser. No. 10/736,188 filed Dec. 15, 2003 which is acontinuation in part of U.S. application Ser. No. 10/379,151 filed onMar. 4, 2003 which, in turn, is a continuation in part of PCT/US01/47931filed on Dec. 10, 2001, which is an international application thatclaims priority to U.S. Provisional Application No. 60/254,113 filedDec. 8, 2000. The entire disclosures of the aforementioned U.S.,international and provisional applications are incorporated herein byreference.

TECHNICAL FIELD

Cancer treatments using a therapy that provides a combination of twomechanisms are disclosed. More specifically, this disclosure relates totreating cancer using a therapy that: 1) interferes with the interactionbetween CD200 and its receptor to block immune suppression therebypromoting eradication of the cancer cells; and 2) directly kills thecancer cells either by a) complement-mediated or antibody-dependentcellular cytotoxicity or b) by targeting cells using a fusion moleculethat includes a CD200-targeting portion.

BACKGROUND

Chronic Lymphocytic Leukemia (CLL) is a disease of the white blood cellsand is the most common form of leukemia in the Western Hemisphere. CLLrepresents a diverse group of diseases relating to the growth ofmalignant lymphocytes that grow slowly but have an extended life span.CLL is classified in various categories that include, for example,B-cell chronic lymphocytic leukemia (B-CLL) of classical and mixedtypes, B-cell and T-cell prolymphocytic leukemia, hairy cell leukemia,and large granular lymphocytic leukemia.

Of all the different types of CLL, B-CLL accounts for approximately 30percent of all leukemias. Although it occurs more frequently inindividuals over 50 years of age, it is increasingly seen in youngerpeople. B-CLL is characterized by accumulation of B-lymphocytes that aremorphologically normal but biologically immature, leading to a loss offunction. Lymphocytes normally function to fight infection. In B-CLL,however, lymphocytes accumulate in the blood and bone marrow and causeswelling of the lymph nodes. The production of normal bone marrow andblood cells is reduced and patients often experience severe anemia aswell as low platelet counts. This can pose the risk of life-threateningbleeding and the development of serious infections because of reducednumbers of white blood cells.

To further understand diseases such as leukemia it is important to havesuitable cell lines that can be used as tools for research on theiretiology, pathogenesis and biology. Examples of malignant humanB-lymphoid cell lines include pre-B acute Iymphoblasticleukemia (Reh),diffuse large cell lymphoma (WSU-DLCL2), and Waldenstrom'smacroglobulinemia (WSU-WM). Unfortunately, many of the existing celllines do not represent the clinically most common types of leukemia andlymphoma.

The use of Epstein Barr Virus (EBV) infection in vitro has resulted insome CLL derived cell lines, in particular B-CLL cells lines, that arerepresentative of the malignant cells. The phenotype of these cell linesis different than that of the in vivo tumors and instead the features ofB-CLL lines tend to be similar to those of Lymphoblastoid cell lines.Attempts to immortalize B-CLL cells with the aid of EBV infection havehad little success. The reasons for this are unclear but it is knownthat it is not due to a lack of EBV receptor expression, binding oruptake. Wells et al. found that B-CLL cells were arrested in the GI/Sphase of the cell cycle and that transformation associated EBV DNA wasnot expressed. This suggests that the interaction of EBV with B-CLLcells is different from that with normal B cells. EBV-transformed CLLcell lines moreover appear to differentiate, possessing a morphologymore similar to Iymphoblastoid cell lines (LCL) immortalized by EBV.

An EBV-negative CLL cell line, WSU-CLL, has been established previously(Mohammad et al., (1996) Leukemia 10(1): 130-7). However, no other suchcell lines are known.

Various mechanisms play a role in the body's response to a diseasestate, including cancer and CLL. For example, CD4⁺T helper cells play acrucial role in an effective immune response against variousmalignancies by providing stimulatory factors to effector cells.Cytotoxic T cells are believed to be the most effective cells toeliminate cancer cells, and T helper cells prime cytotoxic T cells bysecreting Th1 cytokines such as IL-2 and IFN-γ. In various malignancies,T helper cells have been shown to have an altered phenotype compared tocells found in healthy individuals. One of the prominent alteredfeatures is decreased Th1 cytokine production and a shift to theproduction of Th2 cytokines. (See, e.g., Kiani, et al., Haematologica88:754-761 (2003); Maggio, et al., Ann Oncol 13 Suppl 1:52-56 (2002);Ito, et al., Cancer 85:2359-2367 (1999); Podhorecka, et al., Leuk Res26:657-660 (2002); Tatsumi, et al., J Exp Med 196:619-628 (2002);Agarwal, et al., Immunol Invest 32:17-30 (2003); Smyth, et al., Ann SurgOncol 10:455-462 (2003); Contasta, et al., Cancer Biother Radiopharm18:549-557 (2003); Lauerova, et al., Neoplasma 49:159-166(2002).)Reversing that cytokine shift to a Th1 profile has been demonstrated toaugment anti-tumor effects of T cells. (See Winter, et al., Immunology108:409-419 (2003); Inagawa, et al., Anticancer Res 18:3957-3964(1998).)

Mechanisms underlying the capacity of tumor cells to drive the cytokineexpression of T helper cells from Th1 to Th2 include the secretion ofcytokines such as IL-10 or TGF-β as well as the expression of surfacemolecules interacting with cells of the immune system. OX-2/CD200, amolecule expressed on the surface of dendritic cells which possesses ahigh degree of homology to molecules of the immunoglobulin gene family,has been implicated in immune suppression (Gorczynski et al.,Transplantation 65:1106-1114 (1998)) and evidence thatOX-2/CD200-expressing cells can inhibit the stimulation of Th1 cytokineproduction has been provided. Gorczynski et al. demonstrated in a mousemodel that infusion of OX-2/CD200 Fc suppresses the rejection of tumorcells in an animal model using leukaemic tumor cells (Clin Exp Immunol126:220-229 (2001)).

Improved methods for treating individuals suffering from cancer or CLLare desirable, especially to the extent they can enhance the activity ofT cells.

SUMMARY

In one embodiment an CLL cell line of malignant origin is provided thatis not established by immortalisation with EBV. The cell line, which wasderived from primary CLL cells, and is deposited under ATCC accessionno. PTA-3920. In a preferred embodiment, the cell line is CLL-AAT.CLL-AAT is B-CLL cell line, derived from a B-CLL primary cell.

In a further aspect, the CLL-AAT cell line is used to generatemonoclonal antibodies useful in the diagnosis and/or treatment of CLL.Antibodies may be generated by using the cells as disclosed herein asimmunogens, thus raising an immune response in animals from whichmonoclonal antibodies may be isolated. The sequence of such antibodiesmay be determined and the antibodies or variants thereof produced byrecombinant techniques. In this aspect, “variants” includes chimeric,CDR-grafted, humanized and fully human antibodies based on the sequenceof the monoclonal antibodies.

Moreover, antibodies derived from recombinant libraries (“phageantibodies”) may be selected using the cells described herein, orpolypeptides derived therefrom, as bait to isolate the antibodies on thebasis of target specificity.

In a still further aspect, antibodies may be generated by panningantibody libraries using primary CLL cells, or antigens derivedtherefrom, and further screened and/or characterized using a CLL cellline, such as, for example, the CLL cell line described herein.Accordingly, a method for characterizing an antibody specific for CLL isprovided, which includes assessing the binding of the antibody to a CLLcell line.

In a further aspect, there is provided a method for identifying proteinsuniquely expressed in CLL cells employing the CLL-AAT cell line, bymethods well known to those, skilled with art, such as byimmunoprecipitation followed by mass spectroscopy analyses. Suchproteins may be uniquely expressed in the CLL-AAT cell line, or inprimary cells derived from CLL patients.

Small molecule libraries (many available commercially) may be screenedusing the CLL-AAT cell line in a cell-based assay to identify agentscapable of modulating the growth characteristics of the cells. Forexample, the agents may be identified which modulate apoptosis in theCLL-AAT cell line, or which inhibit growth and/or proliferation thereof.Such agents are candidates for the development of therapeutic compounds.

Nucleic acids isolated from CLL-AAT cell lines may be used insubtractive hybridization experiments to identify CLL-specific genes orin micro array analyses (e.g., gene chip experiments). Genes whosetranscription is modulated in CLL cells may be identified. Polypeptideor nucleic acid gene products identified in this manner are useful asleads for the development of antibody or small molecule therapies forCLL.

In a preferred aspect, the CLL-AAT cell line may be used to identifyinternalizing antibodies, which bind to cell surface components whichare internalized by the cell. Such antibodies are candidates fortherapeutic use. In particular, single-chain antibodies, which remainstable in the cytoplasm and which retain intracellular binding activity,may be screened in this manner.

In yet another aspect, a therapeutic treatment is described in which apatient is screened for the presence of a polypeptide that isupregulated by a malignant cancer cell and an antibody that interfereswith the metabolic pathway of the upregulated polypeptide isadministered to the patient.

The present disclosure further is directed to methods wherein adetermination is made as to whether OX-2/CD200 is upregulated in asubject and, if so, administering to the subject a therapy that enhancesimmune response. Upregulation of OX2/CD200 can be determined bymeasuring OX2/CD200 levels directly, or by monitoring the level of anymarker that correlates with OX2/CD200. Suitable immunomodulatorytherapies include the administration of agents that block negativeregulation of T cells or antigen presenting cells, administration ofagents that enhance positive co-stimulation of T cells, cancer vaccines,general adjuvants stimulating the immune system or treatment withcytokines such as IL-2, GM-CSF and IFN-gamma. In particularly usefulembodiments, the therapy that enhances immune response includes theadministration of a polypeptide that binds to OX-2/CD200, optionally incombination with one or more other immunomodulatory therapies. Inanother embodiment, the polypeptide binds to an OX-2/CD200 receptor.

In another aspect, methods in accordance with this disclosure are usedto treat a disease state in which OX-2/CD200 is upregulated in a subjectby administering a polypeptide that binds to OX-2/CD200 or an OX-2/CD200receptor to the subject afflicted with the disease state. In oneembodiment, the disease state treated by these methods includes cancer,specifically, in other embodiments, CLL.

In a particularly useful embodiment, a cancer therapy in accordance withthis disclosure includes i) administering an antibody that interfereswith the interaction between CD200 and its receptor to block immunesuppression, thereby promoting eradication of the cancer cells; and ii)administering a fusion molecule that includes a CD200-targeting portionto directly kill cancer cells. Alternatively, the antibody directlykills the cancer cells through complement-mediated or antibody-dependentcellular cytotoxicity.

In another embodiment in accordance with the present disclosure, methodsare provided for monitoring the progress of a therapeutic treatment. Themethod involves administering a immunomodulatory therapy and determiningOX-2/CD200 levels in a subject at least twice to determine theeffectiveness of the therapy.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates typical steps involved in cell surfacepanning of antibody libraries by magnetically-activated cell sorting(MACS).

FIG. 2 is a graph showing the results of whole cell ELISA demonstratingbinding of selected scFv clones to primary B-CLL cells and absence ofbinding to normal human PBMC. The designation 2°+3° in this and otherfigures refers to negative control wells stained with Mouse Anti-HA anddetecting antimouse antibodies alone. The designation RSC-S Library inthis and other figures refers to soluble antibodies prepared fromoriginal rabbit scFv unpanned library. The designation R3/RSC-S Pool inthis and other figures refers to soluble antibodies prepared from entirepool of scFv antibodies from round 3 of panning. Anti-CD5 antibody wasused as a positive control to verify that equal numbers of B-CLL andPBMC cells were plated in each well.

FIGS. 3 a and 3 b show the results of whole cell ELISA comparing bindingof selected scFv antibodies to primary B-CLL cells and normal primaryhuman B cells. Anti-CD19 antibody was used as a positive control toverify that equal numbers of B-CLL and normal B cells were plated ineach well. Other controls were as described in the legend to FIG. 2.

FIGS. 4 a and 4 b show the results of whole cell ELISA used to determineif scFv clones bind to patient-specific (i.e. idiotype) or bloodtype-specific (i.e. HLA) antigens. Each clone was tested for binding toPBMC isolated from 3 different B-CLL patients. Clones that bound to (1patient sample were considered to be patient or blood type-specific.

FIGS. 5 a and 5 b show the results of whole cell ELISA comparing bindingof scFv clones to primary B-CLL cells and three human leukemic celllines. Ramos is a mature B cell line derived from a Burkitt's lymphoma.RL is a mature B cell line derived from a non-Hodgkin's lymphoma. TF-1is an erythroblastoid cell line derived from a erythroleukemia.

FIGS. 6 a, 6 b and 6 c show the results of whole cell ELISA comparingbinding of scFv clones to primary B-CLL cells and CLL-AAT, a cell linederived from a B-CLL patient. TF-1 cells were included as a negativecontrol.

FIG. 7 shows the binding specificity of scFv antibodies in accordancewith this disclosure as analyzed by 3-color flow cytometry. In normalperipheral blood mononuclear cells, the antigen recognized by scFv-9 ismoderately expressed on B lymphocytes and weakly expressed on asubpopulation of T lymphocytes. PBMC from a normal donor were analyzedby 3-color flow cytometry using anti-CD5-FITC, anti-CD19-PerCP, andscFv-9/Anti-HA-biotin/streptavidin-PE.

FIGS. 8 a, 8 b and 8 c show the expression levels of antigens recognizedby scFv antibodies in accordance with this disclosure. The antigensrecognized by scFv-3 and scFv-9 are overexpressed on the primary CLLtumor from which the CLL-AAT cell line was derived. Primary PBMC fromthe CLL patient used to establish the CLL-AAT cell line or PBMC from anormal donor were stained with scFv antibody and analyzed by flowcytometry. ScFv-3 and scFv-9 stain the CLL cells more brightly than thenormal PBMC as measured by the mean fluorescent intensities.

FIGS. 9A-9C provide a summary of CDR sequences and binding specificitiesof selected scFv antibodies.

FIG. 10 is Table 2 which shows a summary of flow cytometry resultscomparing expression levels of scFv antigens on primary CLL cells vs.normal PBMC as described in FIGS. 8 a-8 c.

FIG. 11 is a Table showing a summary of flow cytometry results comparingexpression levels of scFv-9 antigen with the percentage of CD38+ cellsin peripheral blood mononuclear cells isolated from ten CLL patients.

FIG. 12 shows the identification of scFv antigens by immunoprecipitationand mass spectrometry. CLL-AAT cells were labeled with a solution of 0.5mg/ml sulfo-NHS-LC-biotin (Pierce) in PBS, pH 8.0 for 30′. Afterextensive washing with PBS to remove unreacted biotin, the cells weredisrupted by nitrogen cavitation and the microsomal fraction wasisolated by differential centrifugation. The microsomal fraction wasresuspended in NP40 Lysis Buffer and extensively precleared with normalrabbit serum and protein A sepharose. Antigens were immunoprecipitatedwith HA-tagged scFv antibodies coupled to Rat Anti-HA agarose beads(Roche). Following immunoprecipitation, antigens were separated bySDS-PAGE and detected by Western blot using streptavidin-alkalinephosphatase(AP) or by Coomassie G-250 staining. ScFv-7, an antibodywhich doesn't bind to CLL-AAT cells, was used as a negative control.Antigen bands were excised from the Coomassie-stained gel and identifiedby mass spectrometry (MS). MALDI-MS was performed at the Proteomics CoreFacility of The Scripps Research Institute (La Jolla, Calif.). μLC/MS/MSwas performed at the Harvard Microchemistry Facility (Cambridge, Mass.).

FIG. 13 shows that three scFv antibodies bind specifically to 293-EBNAcells transiently transfected with a human OX-2/CD200 cDNA clone. AOX-2/CD200 cDNA was cloned from CLL cells by RT-PCR and inserted intothe mammalian expression vector pCEP4 (Invitrogen). PCEP4-CD200 plasmidor the corresponding empty vector pCEP4 was transfected into 293-EBNAcells using Polyfect reagent (QIAGEN). Two days after transfection, thecells were analyzed for binding to scFv antibodies by flow cytometry.

FIG. 14 shows that the presence of OX-2/CD200 transfected cells resultedin down-regulation of Th1 cytokines such as IL-2 and IFN-γ. Addition ofthe anti-OX-2/CD200 antibody at 30 μg/ml fully restored the Th1response.

FIG. 15 shows that the presence of CLL cells in a mixed lymphocytereaction resulted in down-regulation of the Th1 response for IL-2.

FIG. 16 shows that the presence of CLL cells in a mixed lymphocytereaction resulted in down-regulation of the Th1 response for IFN-γ.

FIGS. 17A and B show the mean ±SD of tumor volumes for all groups ofNOD/SCID mice were injected subcutaneously with 4×10⁶ RAJI cells eitherin the presence or absence of human.

FIG. 18 shows the results of statistical analyses performed using 2parametric tests (Student's t-test and Welch's test) and onenon-parametric test, the Wilcox test.

FIG. 19A shows ELISA results of representative IgG1 kappa clones afterround 3 panning on CD200-Fc captured on goat anti-mouse IgG Fc antibody.

FIG. 19B shows ELISA results of representative IgG2a kappa clones afterround 3 panning on CD200-Fc captured on goat anti-mouse IgG Fc antibody.

FIG. 19C shows ELISA results of representative IgG1 kappa clones afterround 3 panning on CD200-Fc directly coated on microtiter wells.

FIG. 19D shows ELISA results of representative IgG2a kappa clones afterround 3 panning on CD200-Fc directly coated on microtiter wells.

FIG. 20A shows flow cytometry results of representative IgG1 clonesselected on CD200-Fc captured with goat anti-mouse IgG Fc.

FIG. 20B shows flow cytometry results of representative IgG2a clonesselected on CD200-Fc captured with goat anti-mouse IgG Fc.

FIG. 20C shows flow cytometry results of representative IgG1 clonesselected on directly coated CD200-Fc.

FIG. 20D shows flow cytometry results of representative IgG2a clonesselected on directly coated CD200-Fc.

FIG. 21A shows deduced amino acid sequence of heavy chaincomplementarity regions of CD200-specific clones.

FIG. 21B shows deduced amino acid sequence of heavy chaincomplementarity regions of CD200-specific clones.

FIG. 22 shows ability of selected clones to block the interaction ofCD200 with its receptor (CD200R) in a fluorescent bead assay.

FIG. 23 shows deduced amino acid sequences of selected CD200 Fabs forchimerization.

FIG. 24 shows ELISA results of chimeric IgG obtained from the culturesupernatant of a small-scale transient transfection.

FIG. 25 shows bead inhibition assay results on purified IgG showing thatall antibodies directed against CD200 blocked the receptor ligandinteraction very well.

FIGS. 26A and 26B show that the presence of CLL cells completelyabrogated IFN-gamma and most of IL-2 production observed in the mixedlymphocyte reaction but that the presence of any of the antibodiesallowed for production of these Th1 cytokines.

FIG. 26C shows that IL-10 production was downregulated in the presenceof the antibodies.

FIG. 27 shows the ability to kill CD200 expressing tumor cells in anantibody-dependent cell-mediated cytotoxicity assay (ADCC). All of themouse chimeric CD200 antibodies produced similar levels of lysis whencultured with CD200 positive cells.

DETAILED DESCRIPTION

In accordance with the present disclosure, methods are provided fordetermining whether OX-2/CD200 is upregulated in a subject and, if so,administering to the subject a therapy that enhances immune response.Illustrative examples of suitable immunomodulatory therapies include theadministration of agents that block negative regulation of T cells orantigen presenting cells (e.g., anti-CTLA4 antibodies, anti-PD-L1antibodies, anti-PDL-2 antibodies, anti-PD-1 antibodies and the like) orthe administration of agents that enhance positive co-stimulation of Tcells (e.g., anti-CD40 antibodies or anti 4-1BB antibodies).Furthermore, immunomodulatory therapy could be cancer vaccines such asdendritic cells loaded with tumor cells, tumor RNA or tumor DNA, tumorprotein or tumor peptides, patient derived heat-shocked proteins (hsp's)or general adjuvants stimulating the immune system at various levelssuch as CpG, Luivac, Biostim, Ribominyl, Imudon, Bronchovaxom or anyother compound activating receptors of the innate immune system (e.g.,toll like receptors). Also, immunomodulatory therapy could includetreatment with cytokines such as IL-2, GM-CSF and IFN-gamma.

In particularly useful embodiments, the therapy that enhances immuneresponse is the administration of a polypeptide that binds toOX-2/CD200, alone or in combination with one of the previously mentionedimmunomodulatory therapies. In general, the polypeptides utilized in thepresent disclosure can be constructed using different techniques whichare known to those skilled in the art. In one embodiment, thepolypeptides are obtained by chemical synthesis. In other embodiments,the polypeptides are antibodies or constructed from a fragment orseveral fragments of one or more antibodies.

Preferably, the polypeptides utilized in the methods of the presentdisclosure are obtained from a CLL cell line. “CLL”, as used herein,refers to chronic lymphocytic leukemia involving any lymphocyteincluding, but not limited to, various developmental stages of B cellsand T cells including, but not limited to, B cell CLL (“B-CLL”). B-CLL,as used herein, refers to leukemia with a mature B cell phenotype whichis CD5+, CD23+, CD20^(dim+), sIg^(dim+) and arrested in G0/G1 of thecell cycle. In a further aspect, the CLL cell line is used to generatepolypeptides, including antibodies, useful in the diagnosis and/ortreatment of a disease state in which OX-2/CD200 is upregulated,including cancer and CLL.

As used herein, the term “antibodies” refers to complete antibodies orantibody fragments capable of binding to a selected target. Included areFv, scFv, Fab′ and F(ab′)2, monoclonal and polyclonal antibodies,engineered antibodies (including chimeric, CDR-grafted and humanized,fully human antibodies, and artificially selected antibodies), andsynthetic or semi-synthetic antibodies produced using phage display oralternative techniques. Small fragments, such as Fv and scFv, possessadvantageous properties for diagnostic and therapeutic applications onaccount of their small size and consequent superior tissue distribution.

Antibodies may be generated by using the cells as disclosed herein asimmunogens, thus raising an immune response in animals from whichmonoclonal antibodies may be isolated. The sequence of such antibodiesmay be determined and the antibodies or variants thereof produced byrecombinant techniques. In this aspect, “variants” includes chimeric,CDR-grafted, humanized and fully human antibodies based on the sequenceof the monoclonal antibodies, as well as polypeptides capable of bindingto OX-2/CD200.

Moreover, antibodies derived from recombinant libraries (“phageantibodies”) may be selected using the cells described herein, orpolypeptides derived therefrom, as bait to isolate the antibodies orpolypeptides on the basis of target specificity.

In a still further aspect, antibodies or polypeptides may be generatedby panning antibody libraries using primary CLL cells, or antigensderived therefrom, and further screened and/or characterized using a CLLcell line, such as, for example, the CLL cell line described herein.Accordingly, a method for characterizing an antibody or polypeptidespecific for CLL is provided, which includes assessing the binding ofthe antibody or polypeptide to a CLL cell line.

Preparation of Cell Lines

Cell lines may be produced according to established methodologies knownto those skilled in the art. In general, cell lines are produced byculturing primary cells derived from a patient until immortalized cellsare spontaneously generated in culture. These cells are then isolatedand further cultured to produce clonal cell populations or cellsexhibiting resistance to apoptosis.

For example, CLL cells may be isolated from peripheral blood drawn froma patient suffering from CLL. The cells may be washed, and optionallyimmunotyped in order to determine the type(s) of cells present.Subsequently, the cells may be cultured in a medium, such as a mediumcontaining IL-4. Advantageously, all or part of the medium is replacedone or more times during the culture process. Cell lines may be isolatedthereby, and will be identified by increased growth in culture.

In one embodiment a CLL cell line of malignant origin is provided thatis not established by immortalization with EBV. “Malignant origin”refers to the derivation of the cell line from malignant CLL primarycells, as opposed to non-proliferating cells which are transformed, forexample, with EBV. Cell lines useful according to this disclosure may bethemselves malignant in phenotype, or not. A CLL cell having a“malignant” phenotype encompasses cell growth unattached from substratemedia characterized by repeated cycles of cell growth and exhibitsresistance to apoptosis. The cell line, which was derived from primaryCLL cells, is deposited under ATCC accession no. PTA-3920. In apreferred embodiment, the cell line is CLL-AAT. CLL-AAT is B-CLL cellline, derived from a B-CLL primary cell.

In one embodiment, proteins uniquely expressed in CLL cells areidentified employing the CLL-AAT cell line by methods well known tothose skilled in the art, such as by immunoprecipitation followed bymass spectroscopy analyses. Such proteins may be uniquely expressed inthe CLL-AAT cell line, or in primary cells derived from CLL patients.

Small molecule libraries (many available commercially) may be screenedusing the CLL-AAT cell line in a cell-based assay to identify agentscapable of modulating the growth characteristics of the cells. Forexample, the agents may be identified which modulate apoptosis in theCLL-AAT cell line, or which inhibit growth and/or proliferation thereof.Such agents are candidates for the development of therapeutic compounds.

Nucleic acids isolated from CLL-AAT cell lines may be used insubtractive hybridization experiments to identify CLL-specific genes orin micro array analyses (e.g., gene chip experiments). Genes whosetranscription is modulated in CLL cells may be identified. Polypeptideor nucleic acid gene products identified in this manner are useful asleads for the development of antibody or small molecule therapies forCLL.

In one embodiment, the CLL-AAT cell line may be used to identifyinternalizing antibodies, which bind to cell surface components and arethen internalized by the cell. Such antibodies are candidates fortherapeutic use. In particular, single-chain antibodies, which remainstable in the cytoplasm and which retain intracellular binding activity,may be screened in this manner.

Preparation of Monoclonal Antibodies

Recombinant DNA technology may be used to improve the antibodiesproduced in accordance with this disclosure. Thus, chimeric antibodiesmay be constructed in order to decrease the immunogenicity thereof indiagnostic or therapeutic applications. Moreover, immunogenicity may beminimized by humanizing the antibodies by CDR grafting and, optionally,framework modification. See, U.S. Pat. No. 5,225,539, the contents ofwhich are incorporated herein by reference.

Antibodies may be obtained from animal serum, or, in the case ofmonoclonal antibodies or fragments thereof produced in cell culture.Recombinant DNA technology may be used to produce the antibodiesaccording to established procedure, in bacterial or preferably mammaliancell culture. The selected cell culture system preferably secretes theantibody product.

In another embodiment, a process for the production of an antibodydisclosed herein includes culturing a host, e.g. E. coli or a mammaliancell, which has been transformed with a hybrid vector. The vectorincludes one or more expression cassettes containing a promoter operablylinked to a first DNA sequence encoding a signal peptide linked in theproper reading frame to a second DNA sequence encoding the antibodyprotein. The antibody protein is then collected and isolated.Optionally, the expression cassette may include a promoter operablylinked to polycistronic, for example bicistronic, DNA sequences encodingantibody proteins each individually operably linked to a signal peptidein the proper reading frame.

Multiplication of hybridoma cells or mammalian host cells in vitro iscarried out in suitable culture media, which include the customarystandard culture media (such as, for example Dulbecco's Modified EagleMedium (DMEM) or RPMI 1640 medium), optionally replenished by amammalian serum (e.g. fetal calf serum), or trace elements and growthsustaining supplements (e.g. feeder cells such as normal mouseperitoneal exudate cells, spleen cells, bone marrow macrophages,2-aminoethanol, insulin, transferrin, low density lipoprotein, oleicacid, or the like). Multiplication of host cells which are bacterialcells or yeast cells is likewise carried out in suitable culture mediaknown in the art. For example, for bacteria suitable culture mediainclude medium LE, NZCYM, NZYM, NZM, Terrific Broth, SOB, SOC, 2×YT, orM9 Minimal Medium. For yeast, suitable culture media include medium YPD,YEPD, Minimal Medium, or Complete Minimal Dropout Medium.

In vitro production provides relatively pure antibody preparations andallows scale-up to give large amounts of the desired antibodies.Techniques for bacterial cell, yeast, plant, or mammalian cellcultivation are known in the art and include homogeneous suspensionculture (e.g. in an airlift reactor or in a continuous stirrer reactor),and immobilized or entrapped cell culture (e.g. in hollow fibres,microcapsules, on agarose microbeads or ceramic cartridges).

Large quantities of the desired antibodies can also be obtained bymultiplying mammalian cells in vivo. For this purpose, hybridoma cellsproducing the desired antibodies are injected into histocompatiblemammals to cause growth of antibody-producing tumors. Optionally, theanimals are primed with a hydrocarbon, especially mineral oils such aspristane (tetramethyl-pentadecane), prior to the injection. After one tothree weeks, the antibodies are isolated from the body fluids of thosemammals. For example, hybridoma cells obtained by fusion of suitablemyeloma cells with antibody-producing spleen cells from Balb/c mice, ortransfected cells derived from hybridoma cell line Sp2/0 that producethe desired antibodies are injected intraperitoneally into Balb/c miceoptionally pre-treated with pristine. After one to two weeks, asciticfluid is taken from the animals.

The foregoing, and other, techniques are discussed in, for example,Kohler and Milstein, (1975) Nature 256:495-497; U.S. Pat. No. 4,376,110;Harlow and Lane, Antibodies: a Laboratory Manual, (1988) Cold SpringHarbor, the disclosures of which are all incorporated herein byreference. Techniques for the preparation of recombinant antibodymolecules is described in the above references and also in, for exampleWO97/08320; U.S. Pat. No. 5,427,908; U.S. Pat. No. 5,508,717; Smith,1985, Science, Vol. 225, pp 1315-1317; Parmley and Smith 1988, Gene 73,pp 305-318; De La Cruz et al, 1988, Journal of Biological Chemistry, 263pp 4318-4322; U.S. Pat. No. 5,403,484; U.S. Pat. No. 5,223,409;WO88/06630; WO92/15679; U.S. Pat. No. 5,780,279; U.S. Pat. No.5,571,698; U.S. Pat. No. 6,040,136; Davis et al., Cancer MetastasisRev.,1999;18(4):421-5; Taylor, et al., Nucleic Acids Research 20 (1992):6287-6295; Tomizuka et al., Proc. Nat. Academy of Sciences USA 97(2)(2000): 722-727. The contents of all these references are incorporatedherein by reference.

The cell culture supernatants are screened for the desired antibodies,preferentially by immunofluorescent staining of CLL cells, byimmunoblotting, by an enzyme immunoassay, e.g. a sandwich assay or adot-assay, or a radioimmunoassay.

For isolation of the antibodies, the immunoglobulins in the culturesupernatants or in the ascitic fluid may be concentrated, e.g. byprecipitation with ammonium sulfate, dialysis against hygroscopicmaterial such as polyethylene glycol, filtration through selectivemembranes, or the like. If necessary and/or desired, the antibodies arepurified by the customary chromatography methods, for example gelfiltration, ion-exchange chromatography, chromatography overDEAE-cellulose and/or (immuno-) affinity chromatography, e.g. affinitychromatography with one or more surface polypeptides derived from a CLLcell line according to this disclosure, or with Protein-A or G.

Another embodiment provides a process for the preparation of a bacterialcell line secreting antibodies directed against the cell linecharacterized in that a suitable mammal, for example a rabbit, isimmunized with pooled CLL patient samples. A phage display libraryproduced from the immunized rabbit is constructed and panned for thedesired antibodies in accordance with methods well known in the art(such as, for example, the methods disclosed in the various referencesincorporated herein by reference).

Hybridoma cells secreting the monoclonal antibodies are alsocontemplated. The preferred hybridoma cells are genetically stable,secrete monoclonal antibodies described herein of the desiredspecificity and can be activated from deep-frozen cultures by thawingand recloning.

In another embodiment, a process is provided for the preparation of ahybridoma cell line secreting monoclonal antibodies directed to the CLLcell line is described herein. In that process, a suitable mammal, forexample a Balb/c mouse, is immunized with a one or more polypeptides orantigenic fragments thereof derived from a cell described in thisdisclosure, the cell line itself, or an antigenic carrier containing apurified polypeptide as described. Antibody-producing cells of theimmunized mammal are grown briefly in culture or fused with cells of asuitable myeloma cell line. The hybrid cells obtained in the fusion arecloned, and cell clones secreting the desired antibodies are selected.For example, spleen cells of Balb/c mice immunized with the present cellline are fused with cells of the myeloma cell line PAI or the myelomacell line Sp2/0-Ag 14, the obtained hybrid cells are screened forsecretion of the desired antibodies, and positive hybridoma cells arecloned.

Preferred is a process for the preparation of a hybridoma cell line,characterized in that Balb/c mice are immunized by injectingsubcutaneously and/or intraperitoneally between 10⁶ and 10⁷ cells of acell line in accordance with this disclosure several times, e.g. four tosix times, over several months, e.g. between two and four months. Spleencells from the immunized mice are taken two to four days after the lastinjection and fused with cells of the myeloma cell line PAI in thepresence of a fusion promoter, preferably polyethylene glycol.Preferably, the myeloma cells are fused with a three- to twenty-foldexcess of spleen cells from the immunized mice in a solution containingabout 30% to about 50% polyethylene glycol of a molecular weight around4000. After the fusion, the cells are expanded in suitable culture mediaas described hereinbefore, supplemented with a selection medium, forexample HAT medium, at regular intervals in order to prevent normalmyeloma cells from overgrowing the desired hybridoma cells.

In a further embodiment, recombinant DNA comprising an insert coding fora heavy chain variable domain and/or for a light chain variable domainof antibodies directed to the cell line described hereinbefore areproduced. The term DNA includes coding single stranded DNAs, doublestranded DNAs consisting of said coding DNAs and of complementary DNAsthereto, or these complementary (single stranded) DNAs themselves.

Furthermore, DNA encoding a heavy chain variable domain and/or a lightchain variable domain of antibodies directed to the cell line disclosedherein can be enzymatically or chemically synthesized DNA having theauthentic DNA sequence coding for a heavy chain variable domain and/orfor the light chain variable domain, or a mutant thereof. A mutant ofthe authentic DNA is a DNA encoding a heavy chain variable domain and/ora light chain variable domain of the above-mentioned antibodies in whichone or more amino acids are deleted or exchanged with one or more otheramino acids. Preferably said modification(s) are outside the CDRs of theheavy chain variable domain and/or of the light chain variable domain ofthe antibody in humanization and expression optimization applications.The term mutant DNA also embraces silent mutants wherein one or morenucleotides are replaced by other nucleotides with the new codons codingfor the same amino acid(s). The term mutant sequence also includes adegenerated sequence. Degenerated sequences are degenerated within themeaning of the genetic code in that an unlimited number of nucleotidesare replaced by other nucleotides without resulting in a change of theamino acid sequence originally encoded. Such degenerated sequences maybe useful due to their different restriction sites and/or frequency ofparticular codons which are preferred by the specific host, particularlyE. coli, to obtain an optimal expression of the heavy chain murinevariable domain and/or a light chain murine variable domain.

The term mutant is intended to include a DNA mutant obtained by in vitromutagenesis of the authentic DNA according to methods known in the art.

For the assembly of complete tetrameric immunoglobulin molecules and theexpression of chimeric antibodies, the recombinant DNA inserts codingfor heavy and light chain variable domains are fused with thecorresponding DNAs coding for heavy and light chain constant domains,then transferred into appropriate host cells, for example afterincorporation into hybrid vectors.

Recombinant DNAs including an insert coding for a heavy chain murinevariable domain of an antibody directed to the cell line disclosedherein fused to a human constant domain g, for example γ1, γ2, γ3 or γ4,preferably γ1 or γ4 are also provided. Recombinant DNAs including aninsert coding for a light chain murine variable domain of an antibodydirected to the cell line disclosed herein fused to a human constantdomain κ or λ, preferably κ are also provided

Another embodiment pertains to recombinant DNAs coding for a recombinantpolypeptide wherein the heavy chain variable domain and the light chainvariable domain are linked by way of a spacer group, optionallycomprising a signal sequence facilitating the processing of the antibodyin the host cell and/or a DNA coding for a peptide facilitating thepurification of the antibody and/or a cleavage site and/or a peptidespacer and/or an effector molecule.

The DNA coding for an effector molecule is intended to be a DNA codingfor the effector molecules useful in diagnostic or therapeuticapplications. Thus, effector molecules which are toxins or enzymes,especially enzymes capable of catalyzing the activation of prodrugs, areparticularly indicated. The DNA encoding such an effector molecule hasthe sequence of a naturally occurring enzyme or toxin encoding DNA, or amutant thereof, and can be prepared by methods well known in the art.

Uses of the Present Antibodies/Polypeptides

The polypeptides and/or antibodies utilized herein are especiallyindicated for diagnostic and therapeutic applications.

The present antibodies can be administered as a therapeutic to cancerpatients, especially, but not limited to CLL patients. In someembodiments, the antibodies are capable of interfering with theinteraction of CD200 and its receptors. This interference can block theimmune suppressing effect of CD200. By improving the immune response inthis manner, such antibodies can promote the eradication of cancercells.

The anti-CD200 antibody can also be administered in combination withother immunomodulatory compounds, vaccines or chemotherapy. For example,elimination of existing regulatory T cells with reagents such asanti-CD25 or cyclophosphamide is achieved in one particularly usefulembodiment before starting anti-CD200 treatment. Also, therapeuticefficacy of myeloablative therapies followed by bone marrowtransplantation or adoptive transfer of T cells reactive with CLL cellsare enhanced by anti-CD200 therapy. Furthermore, anti-CD200 treatmentcan substantially enhance efficacy of cancer vaccines such as dendriticcells loaded with CLL cells or proteins, peptides or RNA derived fromsuch cells, patient-derived heat-shocked proteins (hsp's), tumorpeptides or protein. In other embodiments, an, anti-CD200 antibody isused in combination with an immuno-stimulatory compound, such as CpG,toll-like receptor agonists or any other adjuvant, anti-CTLA-4antibodies, and the like. In yet other embodiments, efficacy ofanti-CD200 treatment is improved by blocking of immunosuppressivemechanisms such as anti-PDL1 and/or 2 antibodies, anti-IL-10 antibodies,anti-IL-6 antibodies, and the like.

Anti-CD200 antibodies in accordance with the present disclosure can alsobe used as a diagnostic tool. For example, using blood obtained frompatients with hematopoietic cancers, expression of CD200 can beevaluated on cancer cells by FACS analysis using anti-CD200 antibodiesin combination with the appropriate cancer cell markers such as, e.g.,CD38 and CD19 on CLL cells. Patients with CD200 levels at least 2-foldabove the levels found on normal B cells can be selected for treatmentwith anti-CD200 antibodies.

In another example of using the present anti-CD200 antibodies as adiagnostic tool, biopsies from patients with malignancies are obtainedand expression of CD200 is determined by FACS analysis using anti-CD200antibodies. If tumor cells express CD200 at levels that are at least2-fold higher compared to corresponding normal tissue, cancer patientsare selected for immunomodulatory therapy. Immunomodulatory therapy canbe anti-CD200 therapy, but can also be any other therapy affecting thepatient's immune system. Examples of suitable immunomodulatory therapiesinclude the administration of agents that block negative regulation of Tcells or antigen presenting cells (e.g., anti-CTLA4, anti-PD-L1,anti-PDL-2, anti-PD-1) or the administration of agents that enhancepositive co-stimulation of T cells (e.g., anti-CD40 or anti 4-1BB).Furthermore, immunomodulatory therapy could be cancer vaccines such asdendritic cells loaded with tumor cells, tumor RNA or tumor DNA, tumorprotein or tumor peptides, patient derived heat-shocked proteins (hsp's)or general adjuvants stimulating the immune system at various levelssuch as CpG, Luivac, Biostim, Ribominyl, Imudon, Bronchovaxom or anyother compound activating receptors of the innate immune system (e.g.,toll like receptors). Also, therapy could include treatment withcytokines such as IL-2, GM-CSF and IFN-gamma.

In another embodiment in accordance with the present disclosure, methodsare provided for monitoring the progress and/or effectiveness of atherapeutic treatment. The method involves administering animmunomodulatory therapy and determining OX-2/CD200 levels in a subjectat least twice to determine the effectiveness of the therapy. Forexample, pre-treatment levels of OX-2/CD200 can be ascertained and,after at least one administration of the therapy, levels of OX-2/CD200can again be determined. A decrease in OX-2/CD200 levels is indicativeof an effective treatment. Measurement of OX-2/CD200 levels can be usedby the practitioner as a guide for increasing dosage amount or frequencyof the therapy. It should of course be understood that OX-2/CD200 levelscan be directly monitored or, alternatively, any marker that correlateswith OX-2/CD200 can be monitored.

The present antibodies also may be utilized to detect cancerous cells invivo. This is achieved by labeling the antibody, administering thelabeled antibody to a subject, and then imaging the subject. Examples oflabels useful for diagnostic imaging in accordance with the presentdisclosure are radiolabels such as ¹³¹I, ¹¹¹In, ¹²³I, ⁹⁹mTc, ³²P, ¹²⁵I,³H, ¹⁴C, and ¹⁸⁸Rh, fluorescent labels such as fluorescein andrhodamine, nuclear magnetic resonance active labels, positron emittingisotopes detectable by a positron emission tomography (“PET”) scanner,chemiluminescers such as luciferin, and enzymatic markers such asperoxidase or phosphatase. Short-range radiation emitters, such asisotopes detectable by short-range detector probes, such as atransrectal probe, can also be employed. The antibody can be labeledwith such reagents using techniques known in the art. For example, seeWensel and Meares, Radioimmunoimaging and Radioimmunotherapy, Elsevier,N.Y. (1983), which is hereby incorporated by reference, for techniquesrelating to the radiolabeling of antibodies. See also, D. Colcher etal., “Use of Monoclonal Antibodies as Radiopharmaceuticals for theLocalization of Human Carcinoma Xenografts in Athymic Mice”, Meth.Enzymol. 121: 802-816 (1986), which is hereby incorporated by reference.

A radiolabeled antibody in accordance with this disclosure can be usedfor in vitro diagnostic tests. The specific activity of a antibody,binding portion thereof, probe, or ligand, depends upon the half-life,the isotopic purity of the radioactive label, and how the label isincorporated into the biological agent. In immunoassay tests, the higherthe specific activity, in general, the better the sensitivity.Procedures for labeling antibodies with the radioactive isotopes aregenerally known in the art.

The radiolabeled antibodies can be administered to a patient where it islocalized to cancer cells bearing the antigen with which the antibodyreacts, and is detected or “imaged” in vivo using known techniques suchas radionuclear scanning using e.g., a gamma camera or emissiontomography. See e.g., A. R. Bradwell et al., “Developments in AntibodyImaging”, Monoclonal Antibodies for Cancer Detection and Therapy, R. W.Baldwin et al., (eds.), pp. 65-85 (Academic Press 1985), which is herebyincorporated by reference. Alternatively, a positron emission transaxialtomography scanner, such as designated Pet VI located at BrookhavenNational Laboratory, can be used where the radiolabel emits positrons(e.g., ¹¹C, ¹⁸F, ¹⁵O, and ¹³N).

Fluorophore and chromophore labeled biological agents can be preparedfrom standard moieties known in the art. Since antibodies and otherproteins absorb light having wavelengths up to about 310 nm, thefluorescent moieties should be selected to have substantial absorptionat wavelengths above 310 nm and preferably above 400 nm. A variety ofsuitable fluorescers and chromophores are described by Stryer, Science,162:526 (1968) and Brand, L. et al., Annual Review of Biochemistry,41:843-868 (1972), which are hereby incorporated by reference. Theantibodies can be labeled with fluorescent chromophore groups byconventional procedures such as those disclosed in U.S. Pat. Nos.3,940,475, 4,289,747, and 4,376,110, which are hereby incorporated byreference.

In other embodiments, bispecific antibodies are contemplated. Bispecificantibodies are monoclonal, preferably human or humanized, antibodiesthat have binding specificities for at least two different antigens. Inthe present case, one of the binding specificities is for the CD200antigen on a cancer cell, the other one is for any other antigen, andpreferably for a cell-surface protein or receptor or receptor subunit.

Methods for making bispecific antibodies are within the purview of thoseskilled in the art. Traditionally, the recombinant production ofbispecific antibodies is based on the co-expression of twoimmunoglobulin heavy-chain/light-chain pairs, where the two heavy chainshave different specificities (Milstein and Cuello, Nature, 305:537-539(1983)). Antibody variable domains with the desired bindingspecificities (antibody-antigen combining sites) can be fused toimmunoglobulin constant domain sequences. The fusion preferably is withan immunoglobulin heavy-chain constant domain, including at least partof the hinge, CH2, and CH3 regions. DNAs encoding the immunoglobulinheavy-chain fusions and, if desired, the immunoglobulin light chain, areinserted into separate expression vectors, and are co-transfected into asuitable host organism. For further details of illustrative currentlyknown methods for generating bispecific antibodies see, for example,Suresh et al., Methods in Enzymology, 121:210 (1986); WO 96/27011;Brennan et al., Science 229:81 (1985); Shalaby et al., J. Exy. Med.175:217-225 (1992); Kostelny et al., J. Immunol. 148(5):1547-1553(1992); Hollinger et al., Proc. Natl. Acad. Sci. USA 90:6444-6448(1993); and Gruber et al., J. Immunol. 152:5368 (1994); and Tutt et al.,J. Immunol. 147:60 (1991).

The present antibodies can also be utilized to directly kill or ablatecancerous cells in vivo. This involves administering the antibodies(which are optionally fused to a cytotoxic drug) to a subject requiringsuch treatment. Since the antibodies recognize CD200 on cancer cells,any such cells to which the antibodies bind are destroyed.

Where the antibodies are used alone to kill or ablate cancer cells, suchkilling or ablation can be effected by initiating endogenous host immunefunctions, such as complement-mediated or antibody-dependent cellularcytotoxicity. Assays for determining whether an antibody kills cells inthis manner are within the purview of those skilled in the art.

The antibodies of the present disclosure may be used to deliver avariety of cytotoxic compounds. Any cytotoxic compound can be fused tothe present antibodies. The fusion can be achieved chemically orgenetically (e.g., via expression as a single, fused molecule). Thecytotoxic compound can be a biological, such as a polypeptide, or asmall molecule. As those skilled in the art will appreciate, for smallmolecules, chemical fusion is used, while for biological compounds,either chemical or genetic fusion can be employed.

Non-limiting examples of cytotoxic compounds include therapeutic drugs,a compound emitting radiation, molecules of plants, fungal, or bacterialorigin, biological proteins, and mixtures thereof. The cytotoxic drugscan be intracellularly acting cytotoxic drugs, such as short-rangeradiation emitters, including, for example, short-range, high-energyα-emitters. Enzymatically active toxins and fragments thereof areexemplified by diphtheria toxin A fragment, nonbinding active fragmentsof diphtheria toxin, exotoxin A (from Pseudomonas aeruginosa), ricin Achain, abrin A chain, modeccin A chain, alpha.-sacrin, certain Aleuritesfordii proteins, certain Dianthin proteins, Phytolacca americanaproteins (PAP, PAPII and PAP-S), Morodica charantia inhibitor, curcin,crotin, Saponaria officinalis inhibitor, gelonin, mitogillin,restrictocin, phenomycin, and enomycin, for example. Procedures forpreparing enzymatically active polypeptides of the immunotoxins aredescribed in WO84/03508 and WO85/03508, which are hereby incorporated byreference. Certain cytotoxic moieties are derived from adriamycin,chlorambucil, daunomycin, methotrexate, neocarzinostatin, and platinum,for example.

Procedures for conjugating the antibodies with the cytotoxic agents havebeen previously described and are within the purview of one skilled inthe art.

Alternatively, the antibody can be coupled to high energy radiationemitters, for example, a radioisotope, such as ¹³¹I, a γ-emitter, which,when localized at the tumor site, results in a killing of several celldiameters. See, e.g., S. E. Order, “Analysis, Results, and FutureProspective of the Therapeutic Use of Radiolabeled Antibody in CancerTherapy”, Monoclonal Antibodies for Cancer Detection and Therapy, R. W.Baldwin et al. (eds.), pp 303-316 (Academic Press 1985), which is herebyincorporated by reference. Other suitable radioisotopes includea-emitters, such as ²¹²Bi, ²¹³Bi, and ²¹¹At, and β-emitters, such as¹⁸⁶Re and 90Y.

The route of antibody administration of the present antibodies (whetherthe pure antibody, a labeled antibody, an antibody fused to a toxin,etc.) is in accord with known methods, e.g., injection or infusion byintravenous, intraperitoneal, intracerebral, intramuscular,subcutaneous, intraocular, intraarterial, intrathecal, inhalation orintralesional routes, or by sustained release systems. The antibody ispreferably administered continuously by infusion or by bolus injection.One may administer the antibodies in a local or systemic manner.

The present antibodies may be prepared in a mixture with apharmaceutically acceptable carrier. Techniques for formulation andadministration of the compounds of the instant application may be foundin “Remington's Pharmaceutical Sciences,” Mack Publishing Co., Easton,Pa., latest edition. This therapeutic composition can be administeredintravenously or through the nose or lung, preferably as a liquid orpowder aerosol (lyophilized). The composition may also be administeredparenterally or subcutaneously as desired. When administeredsystematically, the therapeutic composition should be sterile,pyrogen-free and in a parenterally acceptable solution having due regardfor pH, isotonicity, and stability. These conditions are known to thoseskilled in the art.

Pharmaceutical compositions suitable for use include compositionswherein one or more of the present antibodies are contained in an amounteffective to achieve their intended purpose. More specifically, atherapeutically effective amount means an amount of antibody effectiveto prevent, alleviate or ameliorate symptoms of disease or prolong thesurvival of the subject being treated. Determination of atherapeutically effective amount is well within the capability of thoseskilled in the art, especially in light of the detailed disclosureprovided herein. Therapeutically effective dosages may be determined byusing in vitro and in vivo methods.

In some embodiments, present CD200 binding antibodies provide thebenefit of blocking immune suppression in CLL by targeting the leukemiccells directly through CD200. Specifically, stimulating the immunesystem can allow the eradication of CLL cells from the spleen and lymphnodes. Applicants are unaware of any successful eradication of CLL cellsfrom these microenvironments having been achieved with agents thatsimply target B cells (such as alemtuzumab). In contrast, CLL reactive Tcells can have better access to these organs than antibodies. In otherembodiments, direct cell killing is achieved by tagging the CLL cellswith anti-CD200 Abs.

In particularly useful embodiments, the combination of direct cellkilling and driving the immune response towards a Th1 profile provides aparticularly powerful approach to cancer treatment. Thus, in oneembodiments, a cancer treatment is provided wherein an antibody orantibody fragment that binds to CD200 both a) blocks the interactionbetween CD200 and its receptor and b) directly kills the cancer cellsexpressing CD200 is administered to a cancer patient. The mechanism bywhich the cancer cells are killed can include, but are not limited toantibody-dependent cellular cytotoxicity (ADCC) or complement dependentcytotoxicity (CDC); fusion with a toxin; fusion with a radiolabel;fusion with a biological agent involved in cell killing, such asgranzyme B or perforin; fusion with a cytotoxic virus; fusion with acytokine such as TNF-α or IFN-α.

In an alternative embodiment, a cancer treatment involves administeringan antibody that both a) blocks the interaction between CD200 and itsreceptor and b) enhances cytotoxic T cell or NK cell activity againstthe tumor. Such enhancement of the cytotoxic T cell or NK cell activitymay, for example, be combined by fusing the antibody with cytokines suchas e.g. IL-2, IL-12, IL-18, IL-13, IL-5.

In yet another embodiment, the cancer treatment involves administeringan antibody that both a) blocks the interaction between CD200 and itsreceptor and b) attracts T cells to the tumor cells. T cell attractioncan be achieved by fusing the Ab with chemokines such as MIG, IP-10,I-TAC, CCL21, CCL5 or LIGHT. The combined action of blocking immunesuppression and killing directly through antibody targeting of the tumorcells is a unique approach that provides increased efficacy.

While the above disclosure has been directed to antibodies, in someembodiments polypeptides derived from such antibodies can be utilized inaccordance with the present disclosure.

Uses of the CLL Cell Line

There are many advantages to the development of a CLL cell line, as itprovides an important tool for the development of diagnostics andtreatments for CLL, cancer, and other disease states characterized byupregulated levels of OX-2/CD200, e.g., melanoma.

A cell line according to this disclosure may be used for in vitrostudies on the etiology, pathogenesis and biology of CLL and otherdisease states characterized by upregulated levels of OX-2/CD200. Thisassists in the identification of suitable agents that are useful in thetherapy of these diseases.

The cell line may also be used to produce polypeptides and/or monoclonalantibodies for in vitro and in vivo diagnosis of CLL, cancer, and otherdisease states characterized by upregulated levels of OX-2/CD200 (e.g.,melanoma), as referred to above, and for the screening and/orcharacterization of antibodies produced by other methods, such as bypanning antibody libraries with primary cells and/or antigens derivedfrom CLL patients.

The cell line may be used as such, or antigens may be derived therefrom.Advantageously, such antigens are cell-surface antigens specific forCLL. They may be isolated directly from cell lines according to thisdisclosure. Alternatively, a cDNA expression library made from a cellline described herein may be used to express CLL-specific antigens,useful for the selection and characterization of anti-CLL antibodies andthe identification of novel CLL-specific antigens.

Treatment of CLL using monoclonal antibody therapy has been proposed inthe art. Recently, Hainsworth (Oncologist 5 (5) (2000) 376-384) hasdescribed the current therapies derived from monoclonal antibodies.Lymphocytic leukemia in particular is considered to be a good candidatefor this therapeutic approach due to the presence of multiplelymphocyte-specific antigens on lymphocyte tumors.

Existing antibody therapies (such as Rituximab™, directed against theCD20-antigen, which is expressed on the surface of B-lymphocytes) havebeen used successfully against certain lymphocytic disease. However, alower density CD20 antigen is expressed on the surface of B-lymphocytesin CLL (Almasri et al., Am. J. Hematol., 40 (4) (1992) 259-263).

The CLL cell line described herein thus permits the development of novelanti-CLL antibodies and polypeptides having specificity for one or moreantigenic determinants of the present CLL cell line, and their use inthe therapy and diagnosis of CLL, cancer, and other disease statescharacterized by upregulated levels of OX-2/CD200.

The antibody or polypeptide may bind to a receptor with which OX-2/CD200normally interacts, thereby preventing or inhibiting OX-2/CD200 frombinding to the receptor. As yet another alternative, the antibody canbind to an antigen that modulates expression of OX-2/CD200, therebypreventing or inhibiting normal or increased expression of OX-2/CD200.Because the presence of OX-2/CD200 has been associated with reducedimmune response, it would be desirable to interfere with the metabolicpathway of OX-2/CD200 so that the patient's immune system can defendagainst the disease state, such as cancer or CLL, more effectively.

In a particularly useful embodiment, the polypeptide binds toOX-2/CD200. In one embodiment, the polypeptide can be an antibody whichbinds to OX-2/CD200 and prevents or inhibits OX-2/CD200 from interactingwith other molecules or receptors. As CLL cells and other cellsoverexpressing OX-2/CD200 greatly diminish the production of Th1cytokines, the administration of anti-CD200 antibody or a polypeptidewhich binds to OX-2/CD200 to a subject having upregulated levels ofOX-2/CD200 restores the Th1 cytokine profile. Thus, these polypeptidesand/or antibodies can be useful therapeutic agents in the treatment ofCLL and other cancers or diseases over-expressing OX-2/CD200.

Thus, in another embodiment, the method of the present disclosureincludes the steps of screening a subject for the presence OX-2/CD200and administering a polypeptide that binds to OX-2/CD200. It should ofcourse be understood that the presence of OX-2/CD200 can be directlymonitored or, alternatively, any marker that correlates with OX-2/CD200can be detected. In a particularly useful embodiment, a CLL patient isscreened for overexpression of OX-2/CD200 and an antibody that binds toOX-2/CD200 is administered to the patient. As described in detail below,one such antibody is scFv-9 (see FIG. 9B) which binds to OX-2/CD200.

In order that those skilled in the art may be better able to practicethe compositions and methods described herein, the following examplesare given for illustration purposes.

EXAMPLE 1

Isolation of Cell Line CLL-AAT

Establishment of the Cell Line

Peripheral blood from a patient diagnosed with CLL was obtained. The WBCcount was 1.6×10⁸/ml. Mononuclear cells were isolated by Histopaque-1077density gradient centrifugation (Sigma Diagnostics, St. Louis, Mo.).Cells were washed twice with Iscove's Modified Dulbecco's Medium (IMDM)supplemented with 10% heat-inactivated fetal bovine serum (FBS), andresuspended in 5 ml of ice-cold IMDM/10% FBS. Viable cells were countedby staining with trypan blue. Cells were mixed with an equal volume of85% FBS/15% DMSO and frozen in 1 ml aliquots for storage in liquidnitrogen.

Immunophenotyping showed that >90% of the CD45+ lymphocyte populationexpressed IgD, kappa light chain, CD5, CD19, and CD23. This populationalso expressed low levels of IgM and CD20. Approximately 50% of thecells expressed high levels of CD38. The cells were negative for lambdalight chain, CD10 and CD138

An aliquot of the cells was thawed, washed, and resuspended at a densityof 10⁷/mL in IMDM supplemented with 20% heat-inactivated FBS, 2 mML-glutamine, 100 units/ml penicillin, 100 μg/ml streptomycin, 50 μM2-mercaptoethanol, and 5 ng/ml recombinant human IL-4 (R & D Systems,Minneapolis, Minn.). The cells were cultured at 37° C. in a humidified5% CO2 atmosphere. The medium was partially replaced every 4 days untilsteady growth was observed. After 5 weeks, the number of cells in theculture began to double approximately every 4 days. This cell line wasdesignated CLL-AAT.

Characterization of the Cell Line

Immunophenotyping of the cell line by flow cytometry showed highexpression of IgM, kappa light chain, CD23, CD38, and CD138, moderateexpression of CD19 and CD20, and weak expression of IgD and CD5. Thecell line was negative for lambda light chain, CD4, CD8, and CD10.

Immunophenotyping of the cell line was also done by whole cell ELISAusing a panel of rabbit scFv antibodies that had been selected forspecific binding to primary B-CLL cells. All of these CLL-specific scFvantibodies also recognized the CLL-AAT cell line. In contrast, themajority of the scFvs did not bind to two cell lines derived from B celllymphomas: Ramos, a Burkitt's lymphoma cell line, and RL, anon-Hodgkin's lymphoma cell line.

EXAMPLE 2

Selection of scFv Antibodies for B-CLL-Specific Cell Surface Antigensusing Antibody Phage Display and Cell Surface Panning

Immunizations and scFv Antibody Library Construction

Peripheral blood mononuclear cells (PBMC) were isolated from blood drawnfrom CLL patients at the Scripps Clinic (La Jolla, Calif.). Two rabbitswere immunized with 2×10⁷ PBMC pooled from 10 different donors with CLL.Three immunizations, two sub-cutaneous injections followed by oneintravenous injection, were done at three week intervals. Serum titerswere checked by measuring binding of serum IgG to primary CLL cellsusing flow cytometry. Five days after the final immunization, spleen,bone marrow, and PBMC were harvested from the animals. Total RNA wasisolated from these tissues using Tri-Reagent (Molecular ResearchCenter, Inc). Single-chain Fv (scFv) antibody phage display librarieswere constructed as previously described (Barbas et al., (2001) PhageDisplay: A Laboratory Manual, Cold Spring Harbor Laboratory Press, ColdSpring Harbor, N.Y.). For cell surface panning, phagemid particles fromthe reamplified library were precipitated with polyethylene glycol(PEG), resuspended in phosphate-buffered saline(PBS) containing 1%bovine serum albumin (BSA), and dialysed overnight against PBS.

Antibody Selection by Cell Surface Panning

The libraries were enriched for CLL cell surface-specific antibodies bypositive-negative selection with a magnetically-activated cell sorter(MACS) as described by Siegel et al.(1997, J. Immunol. Methods206:73-85). Briefly, phagemid particles from the scFv antibody librarywere preincubated in MPBS (2% nonfat dry milk, 0.02% sodium azide inPBS, pH 7.4) for 1 hour at 25° C. to block nonspecific binding sites.Approximately 10⁷ primary CLL cells were labeled with mouse anti-CD5 IgGand mouse anti-CD19 IgG conjugated to paramagnetic microbeads (MiltenyiBiotec, Sunnyvale, Calif.). Unbound microbeads were removed by washing.The labeled CLL cells (“target cells”) were mixed with an excess of“antigen-negative absorber cells”, pelleted, and resuspended in 50 μl(10¹⁰-10¹¹ cfu) of phage particles. The absorber cells serve to soak upphage that stick non-specifically to cell surfaces as well as phagespecific for “common” antigens present on both the target and absorbercells. The absorber cells used were either TF-1 cells (a humanerythroleukemia cell line) or normal human B cells isolated fromperipheral blood by immunomagnetic negative selection (StemSep system,StemCell Technologies, Vancouver, Canada). The ratio of absorber cellsto target cells was approximately 10 fold by volume. After a 30 minuteincubation at 25° C., the cell/phage mixture was transferred to aMiniMACS MS+ separation column. The column was washed twice with 0.5 mlof MPBS, and once with 0.5 ml of PBS to remove the unbound phage andabsorber cells. The target cells were eluted from the column in 1 ml ofPBS and pelleted in a microcentrifuge at maximum speed for 15 seconds.The captured phage particles were eluted by resuspending the targetcells in 200 μl of acid elution buffer (0.1 N HCl, pH adjusted to 2.2with glycine, plus 1 mg/ml BSA). After a 10 minute incubation at 25° C.,the buffer was neutralized with 12 μL of 2M Tris base, pH 10.5, and theeluted phage were amplified in E. coli for the next round of panning.For each round of panning, the input and output phage titers weredetermined. The input titer is the number of reamplified phage particlesadded to the target cell/absorber cell mixture and the output titer isthe number of captured phage eluted from the target cells. An enrichmentfactor (E) is calculated using the formula E=(R_(n) output/R_(n)input)/(R₁ output/R₁ input). In most cases, an enrichment factor of10²-10³ fold should be attained by the third or fourth round.

Analysis of Enriched Antibody Pools Following Panning

After 3-5 rounds of panning, the pools of captured phage were assayedfor binding to CLL cells by flow cytometry and/or whole cell ELISA:

-   1. To produce an entire pool in the form of HA-tagged soluble    antibodies, 2 ml of a non-suppressor strain of E. coli (e.g.    TOP10F′) was infected with 1 μl (10⁹-10¹⁰ cfu) of phagemid    particles. The original, unpanned library was used as a negative    control. Carbenicillin was added to a final concentration of 10 μM    and the culture was incubated at 37° C. with shaking at 250 rpm for    1 hour. Eight ml of SB medium containing 50 μg/ml carbenicillin was    added and the culture was grown to an OD 600 of ˜0.8. IPTG was added    to a final concentration of 1 mM to induce scFv expression from the    Lac promoter and shaking at 37° C. was continued for 4 hours. The    culture was centrifuged at 3000×g for 15′. The supernatant    containing the soluble antibodies was filtered and stored in 1 ml    aliquots at −20° C.-   2. Binding of the scFv antibody pools to target cells vs. absorber    cells was determined by flow cytometry using high-affinity Rat    Anti-HA (clone 3F10, Roche Molecular Biochemicals) as secondary    antibody and PE-conjugated Donkey Anti-Rat as tertiary antibody.-   3. Binding of the antibody pools to target cells vs. absorber cells    was also determined by whole-cell ELISA as described below.    Screening Individual scFv Clones Following Panning

To screen individual scFv clones following panning, TOP10F′ cells wereinfected with phage pools as described above, spread onto LB platescontaining carbenicillin and tetracycline, and incubated overnight at37° C. Individual colonies were inoculated into deep 96-well platescontaining 0.6-1.0 ml of SB-carbenicillin medium per well. The cultureswere grown for 6-8 hours in a HiGro shaking incubator (GeneMachines, SanCarlos, Calif.) at 520 rpm and 37° C. At this point, a 90 μl aliquotfrom each well was transferred to a deep 96-well plate containing 10 μLof DMSO. This replica plate was stored at −80° C. IPTG was added to theoriginal plate to a final concentration of 1 mM and shaking wascontinued for 3 hours. The plates were centrifuged at 3000×g for 15minutes. The supernatants containing soluble scFv antibodies weretransferred to another deep 96-well plate and stored at −20° C.

A sensitive whole-cell ELISA method for screening HA-tagged scFvantibodies was developed:

-   1. An ELISA plate is coated with concanavalin A (10 mg/ml in 0.1 M    NaHCO₃, pH 8.6, 0.1 mM CaCl₂).-   2. After washing the plate with PBS, 0.5-1×10⁵ target cells or    absorber cells in 50 μl of PBS are added to each well, and the plate    is centrifuged at 250×g for 10 minutes.-   3. 50 μl of 0.02% glutaraldehyde in PBS are added and the cells are    fixed overnight at 4° C.-   4. After washing with PBS, non-specific binding sites are blocked    with PBS containing 4% non-fat dry milk for 3 hours at room    temperature.-   5. The cells are incubated with 50 μl of soluble, HA-tagged scFv or    Fab antibody (TOP10F′ supernatant) for 2 hours at room temperature,    then washed six times with PBS.-   6. Bound antibodies are detected using a Mouse Anti-HA secondary    antibody (clone 12CA5) and an alkaline phosphatase (AP)-conjugated    Anti-Mouse IgG tertiary antibody. An about 10-fold amplification of    the signal is obtained by using AMDEX AP-conjugated Sheep Anti-Mouse    IgG as the tertiary antibody (Amersham Pharmacia Biotech). The AMDEX    antibody is conjugated to multiple AP molecules via a dextran    backbone. Color is developed with the alkaline phosphatase substrate    PNPP and measured at 405 nm using a microplate reader.

Primary screening of the scFv clones was done by ELISA on primary CLLcells versus normal human PBMC. Clones which were positive on CLL cellsand negative on normal PBMC were rescreened by ELISA on normal human Bcells, human B cell lines, TF-1 cells, and the CLL-AAT cell line. Theclones were also rescreened by ELISA on CLL cells isolated from threedifferent patients to eliminate clones that recognized patient-specificor blood type-specific antigens. Results from representative ELISAs areshown in FIGS. 2-6 and summarized in FIGS. 9A-9C.

The number of unique scFv antibody clones obtained was determined by DNAfingerprinting and sequencing. The scFv DNA inserts were amplified fromthe plasmids by PCR and digested with the restriction enzyme BstNI. Theresulting fragments were separated on a 4% agarose gel and stained withethidium bromide. Clones with different restriction fragment patternsmust have different amino acid sequences. Clones with identical patternsprobably have similar or identical sequences. Clones with unique BstNIfingerprints were further analyzed by DNA sequencing. Twenty-fivedifferent sequences were found, which could be clustered into 16 groupsof antibodies with closely related complementarity determining regions(FIGS. 9A-9C).

Characterization of scFv Antibodies by Flow Cytometry

The binding specificities of several scFv antibodies were analyzed by3-color flow cytometry (FIG. 7). PBMC isolated from normal donors werestained with FITC-conjugated anti-CD5 and PerCP-conjugated anti-CD19.Staining with scFv antibody was done using biotin-conjugated anti-HA assecondary antibody and PE-conjugated streptavidin. Three antibodies,scFv-2, scFv-3, and scFv-6, were found to specifically recognize theCD19⁺ B lymphocyte population (data not shown). The fourth antibody,scFv-9, recognized two distinct cell populations: the CD19⁺ Blymphocytes and a subset of CD5⁺ T lymphocytes (FIG. 7). Furthercharacterization of the T cell subset showed that it was a subpopulationof the CD4⁺CD8⁻ TH cells (data not shown).

To determine if the antigens recognized by the scFv antibodies wereoverexpressed on primary CLL cells, PBMC from five CLL patients and fivenormal donors were stained with scFv and compared by flow cytometry(FIG. 8 and Table 2). By comparing the mean fluorescent intensities ofthe positive cell populations, the relative expression level of anantigen on CLL cells vs. normal cells could be determined. One antibody,scFv-2, consistently stained CLL cells less intensely than normal PBMC,whereas scFv-3 and scFv-6 both consistently stained CLL cells morebrightly than normal PBMC. The fourth antibody, scFv-9, stained two ofthe five CLL samples much more intensely than normal PBMC, but gave onlymoderately brighter staining for the other three CLL samples (FIG. 8 andTable 2). This indicates that the antigens for scFv-3 and scFv-6 areoverexpressed approximately 2-fold on most if not all CLL tumors,whereas scFv-9 is overexpressed 3 to 6-fold on a subset of CLL tumors.

CLL patients can be divided into two roughly equal groups: those with apoor prognosis (median survival time of 8 years) and those with afavorable prognosis (median survival time of 26 years). Severalunfavorable prognostic indicators have been identified for CLL, mostnotably the presence of VH genes lacking somatic mutations and thepresence of a high percentage of CD38⁺ B cells. Since scFv-9 recognizesan antigen overexpressed in only a subset of CLL patients, it was soughtto determine if scFv-9 antigen overexpression correlated with thepercentage of CD38⁺ cells in blood samples from ten CLL patients (FIG.11). The results indicate that scFv-9 antigen overexpression and percentCD38⁺ cells are completely independent of one another.

Identification of Antigens Recognized by scFv Antibodies byImmunoprecipitation (IP) and Mass Spectrometry (MS)

To identify the antigens for these antibodies, scFvs were used toimmunoprecipitate the antigens from lysates prepared from the microsomalfraction of cell-surface biotinylated CLL-AAT cells (FIG. 12). Theimmunoprecipitated antigens were purified by SDS-PAGE and identified bymatrix assisted laser desorption ionization mass spectrometry (MALDI-MS)or microcapillary reverse-phase HPLC nano-electrospray tandem massspectrometry (μLC/MS/MS) (data not shown). ScFv-2 immunoprecipitated a110 kd antigen from both RL and CLL-AAT cells (FIG. 12). This antigenwas identified by MALDI-MS as the B cell-specific marker CD19. ScFv-3and scFv-6 both immunoprecipitated a 45 kd antigen from CLL-AAT cells(not shown). This antigen was identified by MALDI-MS as CD23, which is aknown marker for CLL and activated B cells. ScFv-9 immunoprecipitated a50 kd antigen from CLL-AAT cells (FIG. 12). This antigen was identifiedby μLC/MS/MS as OX-2/CD200, a known marker for B cells, activated CD4+ Tcells, and thymocytes. OX-2/CD200 is also expressed on some non-lymphoidcells such as neurons and endothelial cells.

EXAMPLE 3

The capability of cells overexpressing OX-2/CD200 to shift the cytokineresponse from a Th1 response (IL-2, IFN-γ) to a Th2 response (IL-4,IL-10) was assessed in a mixed lymphocyte reaction usingmonocyte-derived macrophages/dendritic cells from one donor andblood-derived T cells from a different donor. As a source ofOX-2/CD200-expressing cells, either OX-2/CD200 transfected EBNA cells asdescribed below or CLL patient samples were used.

Transfection of 293-EBNA Cells

293-EBNA cells (Invitrogen) were seeded at 2.5×10⁶ per 100 mm dish. 24hours later the cells were transiently transfected using Polyfectreagent (QIAGEN) according to the manufacturer's instructions. Cellswere cotransfected with 7.2 μg of OX-2/CD200 cDNA in vector pCEP4(Invitrogen) and 0.8 μg of pAdVAntage vector (Promega). As a negativecontrol, cells were cotransfected with empty pCEP4 vector pluspAdVAntage. 48 hours after transfection, approximately 90% of the cellsexpressed OX-2/CD200 on their surface as determined by flow cytometrywith the scFv-9 antibody.

Maturation of Dendritic Cells/Macrophages from Blood Monocytes

Buffy coats were obtained from the San Diego Blood Bank and primaryblood lymphocytes (PBL) were isolated using Ficoll. Cells were adheredfor 1 hour in Eagles Minimal Essential Medium (EMEM) containing 2% humanserum followed by vigorous washing with PBS. Cells were cultured for 5days either in the presence of GM-CSF, IL-4 and IFN-γ or M-CSF with orwithout the addition of lipopolysaccharide (LPS) after 3 days. Maturedcells were harvested and irradiated at 2000 RAD using a γ-irradiator(Shepherd Mark I Model 30 irradiator (Cs137)).

Mixed Lymphocyte Reaction

Mixed lymphocyte reactions were set up in 24 well plates using 500,000dendritic cells/macrophages and 1×10⁶ responder cells. Responder cellswere T cell enriched lymphocytes purified from peripheral blood usingFicoll. T cells were enriched by incubating the cells for 1 hour intissue culture flasks and taking the non-adherent cell fraction. 500,000OX-2/CD200 transfected EBNA cells or CLL cells were added to themacrophages/dendritic cells in the presence or absence of 30 μg/mlanti-CD200 antibody (scFv-9 converted to full IgG) 2-4 hours before thelymphocyte addition. Supernatants were collected after 48 and 68 hoursand analyzed for the presence of cytokines.

Conversion of scFv-9 to Full IgG

Light chain and heavy chain V genes of scFv-9 were amplified by overlapPCR with primers that connect the variable region of each gene withhuman lambda light chain constant region gene, and human IgG1 heavychain constant region CH1 gene, respectively. Variable regions of lightchain gene and heavy chain gene of scFv-9 were amplified with specificprimers and the human lambda light chain constant region gene and theIgG1 heavy chain constant region CH1 gene were separately amplified withspecific primers as follows: (SEQ ID NO: 103) R9VL-F1 QP: 5′ GGC CTC TAGACA GCC TGT GCT GAC TCA GTC GCC CTC 3′; (SEQ ID NO: 104) R9VL/hCL2-rev:5′ CGA GGG GGC AGC CTT GGG CTG ACC TGT GAC GGT CAG CTG GGT C 3′; (SEQ IDNO: 105) R9VL/hCL2-F: 5′ GAC CCA GCT GAC CGT CAC AGG TCA GCC CAA GGC TGCCCC CTC G 3′; (SEQ ID NO: 106) R9VH-F1: 5′ TCT AAT CTC GAG CAG CAG CAGCTG ATG GAG TCC G 3′; (SEQ ID NO: 107) R9VH/hCG-rev: 5′ GAC CGA TGG GCCCTT GGT GGA GGC TGA GGA GAC GGT GAC CAG GGT GC 3′; (SEQ ID NO: 108)R9VH/hGG-F: 5′ GCA CCC TGG TCA CCG TCT CCT CAG CCT CCA CCA AGG GCC CATCGG TC 3′; (SEQ ID NO: 109) hCL2-rev: 5′ CCA CTG TGA GAG CTC CCG GGT AGAAGT C 3′; (SEQ ID NO: 110) hCG-rev: 5′ GTC ACC GGT TCG GGG AAG TAG TC3′.Amplified Products were Purified and Overlap PCR was Performed.

Final products were digested with Xba I/Sac I (light chain) and XhoI/Pin AI (heavy chain) and cloned into a human Fab expression vector,PAX243hGL (see published International Application WO 2004/078937, thedisclosure of which is incorporated herein by this reference). DNAclones were analyzed for PCR errors by DNA sequencing. The hCMV IEpromoter gene was inserted at Not I/Xho I site (in front of the heavychain). The vector was digested with Xba I/Pin AI/EcoR I/Nhe I and a3472 bp fragment containing the light chain plus the hCMV IE promoterand the heavy chain gene was transferred to an IgG1 expression vector atthe Xba I/Pin AI site.

Cytokine Analysis

The effect of the scFv-9 converted to full IgG on the cytokine profilein the mixed lymphocyte reaction was determined.

Cytokines such as IL-2, IFN-γ, IL-4, IL-10 and IL-6 found in the tissueculture supernatant were quantified using ELISA. Matched capture anddetection antibody pairs for each cytokine were obtained from R+DSystems (Minneapolis, Minn.), and a standard curve for each cytokine wasproduced using recombinant human cytokine. Anti-cytokine captureantibody was coated on the plate in PBS at the optimum concentration.After overnight incubation, the plates were washed and blocked for 1hour with PBS containing 1% BSA and 5% sucrose. After 3 washes with PBScontaining 0.05% Tween, supernatants were added at dilutions of two-foldor ten-fold in PBS containing 1% BSA. Captured cytokines were detectedwith the appropriate biotinylated anti-cytokine antibody followed by theaddition of alkaline phosphatase conjugated streptavidin and SigmaSsubstrate. Color development was assessed with an ELISA plate reader(Molecular Devices).

As shown in FIG. 14, the presence of OX-2/CD200 transfected but notuntransfected cells resulted in down-regulation of Th1 cytokines such asIL-2 and IFN-γ. Addition of the anti-CD200 antibody at 30 μg/ml fullyrestored the Th1 response, indicating that the antibody blockedinteraction of OX-2/CD200 with its receptor.

As set forth in FIGS. 15 and 16, the presence of CLL cells in a mixedlymphocyte reaction resulted in down-regulation of the Th1 response.(FIG. 15 shows the results for IL-2; FIG. 16 shows the results forIFN-γ). This was not only the case for cells over-expressing OX-2/CD200(IB, EM, HS, BH), but also for CLL cells that did not over-expressOX-2/CD200 (JR, JG and GB) (the expression levels for these cells areset forth in FIG. 11). However, the anti-CD200 antibody only restoredthe Th1 response in cells over-expressing OX-2/CD200, indicating thatfor patients over-expressing OX-2/CD200, abrogating OX-2/CD200interaction with its receptor on macrophages was sufficient to restore aTh1 response. In patients that did not over-express OX-2/CD200, othermechanisms appeared to be involved in down-regulating the Th1 response.

Animal Models to Test an Effect of Anti-CD200 on Tumor Rejection

A model was established in which RAJI lymphoma tumor growth is preventedby the simultaneous injection of PBL's. NOD/SCID mice were injectedsubcutaneously with 4×10⁶ RAJI cells either in the presence or absenceof human PBL's from different donors at 1×10⁶, 5×10 ⁶ or 10×10⁶ cells.Tumor length and width as well as body weight was determined 3 times aweek. Mean±SD of tumor volumes for all groups is shown in FIGS. 17A andB. Statistical analysis was performed using 2 parametric tests(Student's t-test and Welch's test) and one non-parametric test, theWilcox test. Results of the statistical analysis are found in FIG. 18.RAJI cells form subcutaneous tumors with acceptable variation. Rejectionis dependent on the specific donor and the PBL cell number. 1×10⁶ PBL'swere insufficient to prevent tumor growth. Donor 2 at 5×10⁶ PBL's fromday 22-43 and donor 3 at 5×10⁶ or 1×10⁷ PBL's starting at day 36significantly reduced tumor growth. Donor 4 is very close to beingsignificant after day 48.

To test for an effect of anti-CD200, RAJI cells are stably transfectedwith CD200. Animals are injected as described in the previous paragraph.In the presence of cD200-transfected cells, tumors grow even in thepresence of human PBL's. Anti-CD200 antibody is administered to evaluatetumor rejection in this model.

Also, a liquid tumor model is established. RAJI cells are injectedintraperitoneally into NOD/SCID mice. Cells disseminate to bone marrow,spleen, lymph node and other organs resulting in paralysis. Concurrentinjection of human PBL's prevents or slows tumor growth. Tumor growth ismonitored by assessing the mice for signs of movement impairment andparalysis. Once these signs are observed, mice are sacrificed and thenumber of tumor cells is assessed in various organs including bonemarrow, spleen, lymph nodes and blood by FACS analysis and PCR.

Similar to the subcutaneous model, CD200 transfected cells are injectedintraperitoneally. They grow even in the presence of human PBL's.Treatment with anti-CD200 results in tumor rejection or slower tumorgrowth.

EXAMPLE 4

Library Construction

A mouse was immunized alternately with baculovirus expressed recombinantCD200 extracellular domain fused to mouse IgG Fc (CD200-Fc) (OrbigenInc., San Diego, Calif.) and 293-EBNA cells transiently transfected witha vector containing full length CD200. Total RNA was prepared from mousespleen using TRI reagent (Molecular Research Center, Inc., Cincinnati,Ohio) according to the manufacturer's protocol. Messenger RNA (mRNA) waspurified using Oligotex (QIAGEN Inc., Valencia, Calif.) according to themanufacturer's manual. First strand cDNA was synthesized usingSuperScript II RTase (Invitrogen Life Technologies, Carlsbad, Calif.)according to the manufacturer's protocol. First strand cDNA was digestedwith restriction endonuclease and second strand cDNA was synthesizedaccording to the method fully described in published PCT applicationWO03/025202A2, published Mar. 27, 2003. Second strand cDNA was cleanedup with PCR purification kit (QIAGEN) and single primer amplificationwas performed according to the method described in published PCTapplication WO03/025202A2, published Mar. 27, 2003. Amplified productswere pooled and purified with PCR purification kit. Kappa light chainwas digested with Xba I and BspE I, and IgG1 and IgG2a heavy chains weredigested with Xho I and Bln I. Digested fragments were purified from theagarose gel using Gel extraction kit (QIAGEN) and cloned into PAX313m/hG vector as described in published PCT application WO/04078937A2published Sep. 16, 2004.

Library Panning

The libraries (IgG1 kappa and IgG2a kappa) were panned on CD200-Fceither directly coated on the microtiter wells (Costar Group, Bethesda,Md.) or captured with goat anti-mouse IgG Fc specific antibody(Sigma-Aldrich Corp., St. Louis, Mo.). For the preparation of libraryphage, electrocompetent XL1-Blue cells (Stratagene, La Jolla, Calif.)were electroporated with library DNA and grown in SOC medium for 1 hourand in SB medium for 2 hours with carbenicillin. Phage production wasinduced with the addition of VCS M13 helper phage (Amersham BiosciencesCorp., Piscataway, N.J.) and 1 mM IPTG at 30° C. overnight. The culturewas spun down and phage was precipitated with 4% polyethylene glycol and3% NaCl. The phage was spun down and resuspended in 1% BSA/PBScontaining unrelated antigen, FLJ32028 that is also baculovirusexpressed extracellular domain fused to mouse IgG Fc (FLJ32028-Fc)(Orbigen, San Diego), as a soluble competitor. For the panning ondirectly coated CD200-Fc, four wells were coated with 100 μl of CD200-Fc(5 μg/ml in 0.1 M NaHCO₃ pH 8.6) at 4° C. overnight. The wells werewashed 5 times with phosphate buffered saline (PBS) pH 7.0 and blockedwith 1% bovine serum albumin (BSA)/PBS at 37° C. for 1 hr. For thepanning on CD200-Fc captured on goat anti-mouse IgG Fc, four microtiterwells were coated with 100 μl goat anti-mouse IgG Fc (20 μg/ml in PBS)at 4° C. overnight. The wells were washed 5 times with PBS and incubatedwith 100 μl CD200-Fc (20 μg/ml in PBS) for 1 hour at 37° C. The wellswere washed 5 times with PBS and blocked with 1% BSA/PBS at 37° C. for 1hour. For both panning, the blocker was replaced with the mixture ofsoluble Fabs obtained from the panning of another library (the librarydescribed in Example 3 of PCT application Ser. No. PCT/US04/17118 filedJun. 2, 2004 (not yet published), the entire disclosure of which isincorporated herein by this reference) on FLJ32028 to mask epitopes onmouse IgG Fc and the wells were incubated for 30 min at 37° C. Thesemasking Fabs were shown to also bind to CD200-Fc. Library phage wasadded on top of the masking Fabs and the wells were incubated forapproximately 1.5 hours at 37° C. The unbound phage was washed with PBSwith increasing stringency (3 times in the first round, 5 times in the2^(nd) round and 10 times in the 3^(rd) and the 4^(th) rounds) with 5minute incubation and pipetting up and down 5 times for each wash. Thebound phage was eluted twice with 100 μl 0.1 M HCl with 1 mg/ml BSA,pH2.2 and neutralized with 2 M Tris Base pH 11.5. The freshly grownER2738 cells were infected with eluted phage and titrated onto LBagarose plates containing carbenicillin and glucose. The remaining phagewas propagated overnight at 30-37° C. with the addition of VCS M13helper phage and 1 mM IPTG for the next round of panning.

Library Screening

Ninety five colonies from round 3 and 4 titration plates were grown in 1ml SB containing 12.5 μg/ml tetracycline and 50 μg/ml carbenicillin forapproximately 6 hours at 37° C. VCS M13 helper phage was added and theculture was incubated for 2 hours at 37° C. 1 mM IPTG and 70 μg/mlkanamycin were added and Fab-phage production was induced at 30° C.overnight. Microtiter wells were coated with 50 μl of rabbit anti-mouseIgG F(ab′)2 (4 μg/ml in PBS), CD200-Fc (4 μg/ml in 0.1 M NaHCO3 pH 8.6),or FLJ32028-Fc (4 μg/ml in 0.1 M NaHCO3 pH 8.6) at 4° C. overnight. Thewells were washed 3 times with PBS and blocked with 100 μl 1% BSA/PBSfor 1 hour at 37° C. The culture was spun down. The blocker was replacedwith the culture supernatant containing Fab-phage and the wells wereincubated for 1.5˜2 hours at 37° C. The remaining Fab-phage was storedat −80° C. for flow cytometry. The plates were washed 3 times with PBSand the binding was detected with 50 μl alkaline phosphatase(AP)-conjugated goat anti-mouse IgG F(ab′)2 antibody (Pierce)(1:500 in1% BSA/PBS) for 1 hr at 37° C. The plates were washed 3 times with PBSand developed with AP substrate (Sigma-Aldrich) in pNPP buffer. Almostall of the clones from round 3 were already specifically positive toCD200 (FIG. 19A-D). Clones were also screened by high throughput flowcytometry analysis. One hundred micro-liter 293 cells transientlytransfected with CD200 (1×10⁵ cells) were aliquoted into 96 well plate(Costar). Fifty micro-liter Fab-phage was added to the cells and mixedby pipetting and incubated on ice for 30 minutes. The cells were washedtwice with 1% BSA/PBS containing 0.01% NaN3. The cells were resuspendedin 100 μl PE-conjugated goat anti-mouse IgG antibody (Sigma-Aldrich) in1% BSA/PBS containing 0.01% NaN3 and incubated on ice for 30 minutes.The cells were washed twice with 1% BSA/PBS containing 0.01% NaN3 andresuspended in 200 μl 1% paraformaldehyde in PBS. Representative clonesshowing positive binding to CD200 expressing cells are shown in FIG.20A-D.

DNA sequences were analyzed and deduced amino acid sequences of theheavy chain were grouped according to the complementarity determiningregion 3 (CDR3) (FIGS. 21A, B). They were divided into 17 groups.

Fluorescent Bead Assay

23 clones were selected for further analysis. They were cG2aR3B5,dG1R3A5, cG2aR3A2, dG2aR3B2, dG1R3A1, cG2aR3A1, cG2aR3B, dG1R3B, cG1R3A,cG1R3A, cG1R3A1, dG1R3B, dG1R3B, cG1R3C, dG2aR3C, dG2aR3A1, cG2aR3B,cG2aR3B, dG1R3B, cG2aR3B, cG2aR3C, dG1R3H, and dG2aR3A6. DNA of selectedFabs were digested with Spe I/Nhe I for gene III removal and soluble Fabexpression and purification. The purified Fabs were evaluated for theirability to block the interaction of CD200 with its receptor (CD200R) ina fluorescent bead assay. TransFluoSpheres carboxylate-modifiedmicrospheres (488/645) (Molecular Probes Invitrogen DetectionTechnologies, Eugene, Oreg.) were coated with streptavidin followed by abiotin-labeled anti-human Fc antibody and baculovirus-produced CD200-Fcprotein. 293 cells were transiently transfected with CD200R. Cellsurface expression was confirmed by FACS analysis. 1 millionCD200-coated beads were pre-incubated with various amounts of anti-CD200Fabs or chimeric IgG for 10 minutes before the addition of 50,000 CD20ORtransfected cells. After 30 minute incubation at 37° C., the cells werewashed in Tris buffer containing 1% BSA and analyzed using a FACSCalibur. Fabs c1A10, c2aB7, and d1A5 showed the best blocking of CD200and CD200R interaction at 6.7 μg/ml of Fab (FIG. 22). These clones arereferred to as cG1R3A10, cG2aR3B7 and dG1R3A5, respectively in FIGS. 21Aand/or B.

Chimerization and IgG Conversion

Six antibodies were selected for chimerization and IgG conversion. (SeeFIG. 23.) They were c1A10 (cG1R3A10), c2aA10 (cG2aR3A10), c2aB7(cG2aR3B7), d1A5 (dG1R3A5), d1BS (dG1R3B5), and d1B10 (dG1R3B10). Forthe chimerization, overlap PCR was performed to connect mouse kappachain variable region and human kappa chain constant region. Mouse heavychain variable region was amplified with a 3′ primer that contains apartial human IgG1 constant region and Apa I site for cloning. Amplifiedkappa chain fragments and heavy chain fragments were cloned intoPAX243hGK vector (see published International Application WO2004/078937) that contains human IgG1 constant region at Xba I/Not I forkappa light chain and Xho I/Apa I for heavy chain fragment. Binding ofchimeric Fab to CD200 was confirmed by ELISA and flow cytometry. Thesechimeric Fabs were converted into IgG by insertion of humancytomegalovirus immediate early promoter (hCMV IE Pro) sequence for theheavy chain expression at Not I/Xho I, then the transfer of the lightchain and heavy chain into a human IgG1 expression vector at Xba I/PinAI sites. This vector has an additional hCMV IE Pro sequence upstreamXba I site for the light chain expression in mammalian cells. The DNAsequences were confirmed and maxi prep DNA was prepared using HiSpeedMaxi prep columns (QIAGEN) for mammalian cell transfection. Transienttransfection was performed in 293-EBNA cells using Effectene (QIAGEN)according to the manufacturer's protocol with the addition of pAdVAntagevector (Promega US, Madison, Wis.). Stable cell line transfection wasperformed in NS0 cells using Effectene according to the manufacturer'sprotocol. After a small scale transient transfection, culturesupernatant for each antibody was tested by ELISA (FIG. 24). After alarge scale transient transfection, each IgG was purified from theculture supernatant by anti-human IgG F(ab′)2 affinity column using FPLC(Amersham Biosciences).

The purified IgG were tested in bead inhibition assay as described forthe Fab's. All antibodies directed against CD200 blocked the receptorligand interaction very well as shown below in FIG. 25.

Mixed Lymphocyte Reaction

Whether blocking of CD200 interaction with its receptor also preventsthe cytokine shift from Th1 to Th2 observed in mixed lymphocytesreactions in the presence of CD200 was evaluated. Buffy coats wereobtained from the San Diego Blood Bank and primary blood lymphocytes(PBL) were isolated using Histopaque (Sigma-Aldrich). Cells were adheredfor 1 h in EMEM containing 2% human serum followed by vigorous washingwith PBS. Cells were cultured for 5 days in the presence of GM-CSF, IL-4and IFN-γ. Matured cells were harvested and irradiated at 2000 RAD usinga γ-irradiator (University of California San Diego). Mixed lymphocytereactions were set up in 24 well plates using 500,000 dendritic cellsand 1×10⁶ responder cells. Responder cells were T cell enrichedlymphocytes purified from peripheral blood using Histopaque. T cellswere enriched by incubating the cells for 1 hour in tissue cultureflasks and taking the non-adherent cell fraction. Five hundred thousandCD200 expressing primary irradiated CLL cells were added to thedendritic cells in the presence or absence of various amounts ofanti-CD200 antibodies 2-4 hours before the lymphocyte addition.Supernatants were collected after 48 and 68 hours and cytokines such asIL-2, IFN-γ, IL-4, IL-10 and IL-6 were quantified using ELISA. Matchedcapture and detection antibody pairs for each cytokine were obtainedfrom R+D Systems (Minneapolis), and a standard curve for each cytokinewas produced using recombinant human cytokine. Anti-cytokine captureantibody was coated on the plate in PBS at the optimum concentration.After overnight incubation, the plates were washed and blocked for 1 hwith PBS containing 1% BSA and 5% sucrose. After 3 washes with PBScontaining 0.05% Tween, supernatants were added at the indicateddilutions in PBS containing 1% BSA. Captured cytokines were detectedwith the appropriate biotinylated anti-cytokine antibody followed by theaddition of alkaline phosphatase conjugated streptavidin and SigmaSsubstrate. Color development was assessed with an ELISA plate reader(Molecular Devices Corp., Sunnyvale, Calif.). As shown in the FIGS. 26A,B, the presence of CLL cells completely abrogated IFN-gamma and most ofIL-2 production observed in the mixed lymphocyte reaction. Presence ofany of the antibodies allowed for production of these Th1 cytokines(FIGS. 26A, B). In contrast, IL-10 production was downregulated in thepresence of the antibodies. (See FIG. 26C.)

Antibody-Dependent Cell-Mediated Cytotoxicity Assay

Furthermore, the six chimeric mouse anti-CD200 antibodies were evaluatedfor their ability to kill CD200 expressing tumor cells in anantibody-dependent cell-mediated cytotoxicity assay (ADCC). 293-EBNAcells transfected with CD200 were labeled with 100 μCi/million cells in0.5 ml medium for 1 hr at 37° C. After 3 washes, cells were counted,resuspended in medium (RPMI supplemented with 10% human AB serum) at 0.2million/ml and 50 μl (10,000 cells/well) was dispensed in triplicateinto a 96 well round bottom plate. 20 μl of anti-CD200 antibodies weredispensed into each well so as to achieve a final concentration of 20μg/ml. Peripheral blood mononuclear cells (effector cells) were isolatedon a Ficoll gradient, red blood cells were lysed with ammonium chloride,washed and resuspended in culture medium and 50 μl of cells weredispensed into each well. The assay plates were spun (1,500 rpm/5minutes/low brake) and transferred to the cell culture incubator. After4 hours, assay plates were spun as before. 36 μl of the supernatantswere transferred to pico plates and mixed with 250 μl microscint-20cocktail, and placed on the orbital shaker for 2 minutes and read on aTop count. As illustrated in the FIG. 27, all of the mouse chimericCD200 antibodies produced similar levels of lysis when cultured withCD200 positive cells. No lysis was observed with CD200 negative cells.In addition, the extent of lysis was statistically significant (p<0.05)when compared to isotype control antibody, d2A6 (anti-FLJ32028antibody).

REFERENCES

The following references are incorporated herein by reference to morefully describe the state of the art to which the present inventionpertains. Any inconsistency between these publications below or thoseincorporated by reference above and the present disclosure shall beresolved in favor of the present disclosure.

-   1) Agarwal, et al., (2003). Disregulated expression of the Th2    cytokine gene in patients with intraoral squamous cell carcinoma.    Immunol Invest 32:17-30.-   2) Almasri, N M et al. (1992). Am J Hematol40 259-263.-   3) Contasta, et al., (2003). Passage from normal mucosa to adenoma    and colon cancer: alteration of normal sCD30 mechanisms regulating    TH1/TH2 cell functions. Cancer Biother Radiopharm 18:549-557.-   4) Gorczynski, et al., (1998). Increased expression of the novel    molecule OX-2 is involved in prolongation of murine renal allograft    survival. Transplantation 65:1106-1114.-   5) Gorczynski, et al., (2001). Evidence of a role for CD200 in    regulation of immune rejection of leukaemic tumour cells in C57BL/6    mice. Clin Exp Immunol 126:220-229.-   6) Hainsworth, J D (2000). Oncologist 2000; 5(5):376-84.-   7) Inagawa, et al., (1998). Mechanisms by which chemotherapeutic    agents augment the antitumor effects of tumor necrosis factor:    involvement of the pattern shift of cytokines from Th2 to Th1 in    tumor lesions. Anticancer Res 18:3957-3964.-   8) Ito, et al., (1999). Lung carcinoma: analysis of T helper type 1    and 2 cells and T cytotoxic type 1 and 2 cells by intracellular    cytokine detection with flow cytometry. Cancer 85:2359-2367.-   9) Kiani, et al., (2003). Normal intrinsic Th1/Th2 balance in    patients with chronic phase chronic myeloid leukemia not treated    with interferon-alpha or imatinib. Haematologica 88:754-761.-   10) Lauerova, et al., (2002). Malignant melanoma associates with    Th1/Th2 imbalance that coincides with disease progression and    immunotherapy response. Neoplasma 49:159-166.-   11) Maggio, et al., (2002). Chemokines, cytokines and their    receptors in Hodgkin's lymphoma cell lines and tissues. Ann Oncol 13    Suppl 1:52-56.-   12) Nilsson, K (1992). Burn Cell. 5(1):25-41.-   13) Podhorecka, et al., (2002). T type 1/type 2 subsets balance in    B-cell chronic lymphocytic leukemia—the three-color flow cytometry    analysis. Leuk Res 26:657-660.-   14) Pu, Q Q and Bezwoda, W (2000). Anticancer Res. 20(4):2569-78.-   15) Smyth, et al., (2003). Renal cell carcinoma induces    prostaglandin E2 and T-helper type 2 cytokine production in    peripheral blood mononuclear cells. Ann Surg Oncol 10:455-462.-   16) Tatsumi, et al., (2002). Disease-associated bias in T helper    type 1 (Th1)/Th2 CD4(+) T cell responses against MAGE-6 in    HLA-DRB10401(+) patients with renal cell carcinoma or melanoma. J    Exp Med 196:619-628.-   17) Walls A Vet al. (1989). Int. J Cancer 44846-853.-   18) Winter, et al., (2003). Tumour-induced polarization of tumour    vaccine-draining lymph node T cells to a type 1 cytokine profile    predicts inherent strong immunogenicity of the tumour and correlates    with therapeutic efficacy in adoptive transfer studies. Immunology    108:409-419.

It will be understood that various modifications may be made to theembodiments disclosed herein. For example, as those skilled in the artwill appreciate, the specific sequences described herein can be alteredslightly without necessarily adversely affecting the functionality ofthe polypeptide, antibody or antibody fragment used in bindingOX-2/CD200. For instance, substitutions of single or multiple aminoacids in the antibody sequence can frequently be made without destroyingthe functionality of the antibody or fragment. Thus, it should beunderstood that polypeptides or antibodies having a degree of homologygreater than 70% to the specific antibodies described herein are withinthe scope of this disclosure. In particularly useful embodiments,antibodies having a homology greater than about 80% to the specificantibodies described herein are contemplated. In other usefulembodiments, antibodies having a homology greater than about 90% to thespecific antibodies described herein are contemplated. Therefore, theabove description should not be construed as limiting, but merely asexemplifications of preferred embodiments. Those skilled in the art willenvision other modifications within the scope and spirit of thisdisclosure.

1. An antibody that binds to a cell that expresses CD200 comprising apolypeptide sequence selected from the group consisting of SEQ ID NOS:111-199.
 2. An antibody as in claim 1 comprising a polypeptide sequenceselected from the group consisting of SEQ ID NOS: 111, 114, 118, 133,136, 140, 141, 149, 155, 162, 163, 165, 174, 181, 187, 188, 189, 195 and199.
 3. An antibody as in claim 1 comprising a polypeptide sequenceselected from the group consisting of SEQ ID NOS: 200-205.
 4. Anantibody as in claim 1 wherein the antibody comprises a humanizedantibody.
 5. An antibody as in claim 1 wherein the antibody comprises anFv, scFv, Fab′ and F(ab′)2.
 6. A method of treating cancer comprising:administering to a subject afflicted with cancer a therapeuticcomposition that contains an antibody that binds to a cell thatexpresses CD200, the antibody being present in an amount sufficient topromote production of one or more Th1 cytokines.
 7. A method as in claim6 wherein the antibody comprises a polypeptide sequence selected fromthe group consisting of SEQ ID NOS: 111-199.
 8. A method as in claim 6wherein the antibody comprises a polypeptide sequence selected from thegroup consisting of SEQ ID NOS: 111, 114, 118, 133, 136, 140, 141, 149,155, 162, 163, 165, 174, 181, 187, 188, 189, 195 and
 199. 9. A method asin claim 6 wherein the antibody comprises polypeptide sequence selectedfrom the group consisting of SEQ ID NOS: 200-211.
 10. A method as inclaim 6 wherein the antibody comprises a humanized antibody.
 11. Amethod as in claim 6 wherein the antibody comprises an Fv, scFv, Fab′and F(ab′)2.
 12. A method as in claim 6 wherein the cancer is CLL.
 13. Amethod of killing tumor cells comprising: administering to a subjectafflicted with cancer a therapeutic composition that contains anantibody that binds to a cell that expresses CD200, the antibody beingpresent in an amount sufficient to cause antibody-dependentcell-mediated cytotoxicity.
 14. A method as in claim 13 wherein theantibody comprises a polypeptide sequence selected from the groupconsisting of SEQ ID NOS: 111-199.
 15. A method as in claim 13 whereinthe antibody comprises a polypeptide sequence selected from the groupconsisting of SEQ ID NOS: 111, 114, 118, 133, 136, 140, 141, 149, 155,162, 163, 165, 174, 181, 187, 188, 189, 195 and
 199. 16. A method as inclaim 13 wherein the antibody comprises a polypeptide sequence selectedfrom the group consisting of SEQ ID NOS: 200-211.
 17. A method as inclaim 13 wherein the antibody comprises a humanized antibody.
 18. Amethod as in claim 13 wherein the antibody comprises an Fv, scFv, Fab′and F(ab′)2.
 19. A method as in claim 13 wherein the cancer is CLL. 20.A fusion molecule comprising: a first portion that targets cells bearingthe OX-2/CD200 antigen, the first portion comprising a polypeptidesequence selected from the group consisting of SEQ ID NOS: 111-199; anda second portion that promotes the death of cells.
 21. A fusion moleculeas in claim 20 wherein the first portion comprises a polypeptidesequence selected from the group consisting of SEQ ID NOS: 111, 114,118, 133, 136, 140, 141, 149, 155, 162, 163, 165, 174, 181, 187, 188,189, 195 and
 199. 22. A fusion molecule as in claim 20 wherein the firstportion comprises a polypeptide sequence selected from the groupconsisting of SEQ ID NOS: 200-211.
 23. A composition comprising anantibody comprising a polypeptide sequence selected from the groupconsisting of SEQ ID NOS: 111-199 and a pharmaceutically acceptablecarrier.
 24. A composition as in claim 23 wherein the antibody comprisesa humanized antibody.
 25. A composition as in claim 23 wherein theantibody comprises an Fv, scFv, Fab′ and F(ab′)2.
 26. A method oftreating cancer comprising: administering to a subject afflicted withcancer a therapeutic composition that contains an antibody that binds toa cell that expresses CD200, the antibody being present in an amountsufficient to promote production of one or more Th1 cytokines and tocause complement-mediated or antibody-dependent cellular cytotoxicity.27. A chimeric antibody that binds to a cell that expresses CD200comprising a polypeptide sequence selected from the group consisting ofSEQ ID NOS: 200-211.
 28. A method comprising: determining whetherOX-2/CD200 is upregulated in a subject; and administering to the subjectof a therapy that enhances immune response.
 29. A method as in claim 28wherein the therapy comprises administering a polypeptide that binds toOX-2/CD200 or an OX-2/CD200 receptor, the polypeptide being administeredin an amount effective to inhibit the immune-suppressing effect ofOX-2/CD200.
 30. A method as in claim 28 wherein the subject is a cancerpatient.
 31. A method as in claim 28 wherein the subject is a CLLpatient.
 32. A method as in claim 29 wherein the polypeptide comprisesan antibody.
 33. A method as in claim 29 wherein the polypeptidecomprises a humanized antibody.
 34. A method as in claim 29 wherein thepolypeptide comprises an Fv, scFv, Fab′ and F(ab′)2.
 35. A method as inclaim 28 wherein the step of determining whether OX-2/CD200 isupregulated in a subject comprises: obtaining tissue from a cancerpatient; evaluating whether CD200 levels are at least 2-fold above thelevels found on corresponding normal tissue.
 36. A method as in claim 35wherein blood is the tissue obtained from a cancer patient.
 37. A methodas in claim 35 wherein tissue is obtained from a cancer patient byperforming a biopsy.
 38. A method as in claim 35 wherein CD200 levelsare evaluated by conducting FACS analysis using anti-CD200 antibodies incombination with cancer cell markers.
 39. A method as in claim 35wherein the cancer cell marker is CD38 or CD19.
 40. A method as in claim35 wherein the patient is afflicted with a hematopoietic cancer.
 41. Amethod as in claim 35 wherein the patient is afflicted with CLL.
 42. Amethod as in claim 29 wherein the therapy comprises eliminating existingregulatory T cells prior to administering a polypeptide that binds toOX-2/CD200 or an OX-2/CD200 receptor, the polypeptide being administeredin an amount effective to inhibit the immune-suppressing effect ofOX-2/CD200.
 43. A method as in claim 42 wherein the therapy comprisesadministering a regulatory T cell eliminating amount of a reagentselected form the group consisting of anti-CD25 antibodies andcyclophosphamide.
 44. A method as in claim 29 wherein the therapyfurther comprises administering a myeloablative therapy.
 45. A method asin claim 44 wherein the therapy further comprises a bone marrowtransplant.
 46. A method as in claim 44 wherein the therapy furthercomprises a transfer of CLL reactive T cells.
 47. A method as in claim29 wherein the therapy further comprises administering a cancer vaccine.48. A method as in claim 47 wherein the cancer vaccine is selected fromthe group consisting of dendritic cells loaded with CLL cells orproteins, peptides or RNA derived from dendritic cells loaded with CLLcells, patient-derived heat-shocked proteins, tumor peptides and tumorproteins.
 49. A method as in claim 29 wherein the therapy furthercomprises administering an effective immune stimulating amount of animmuno-stimulatory compound.
 50. A method as in claim 49 wherein theimmuno-stimulatory compound is selected from the group consisting ofCpG, toll-like receptor agonists and anti-CTLA-4 antibodies.
 51. Amethod as in claim 29 wherein the therapy further comprisesadministering an effective immunosuppressive blocking amount of acompound selected from the group consisting of anti-PDL1 antibodies,anti-PDL1 antibodies, anti-IL-10 antibodies and anti-IL-6 antibodies.52. A method as in claim 29 wherein the therapy comprises administeringan effective amount of an agent capable of blocking negative regulationof T cells or antigen presenting cells.
 53. A method as in claim 52wherein the agent is selected from the group consisting of anti-CTLA4antibodies, anti-PD-L1 antibodies, anti-PDL-2 antibodies and anti-PD-1antibodies.
 54. A method as in claim 29 wherein the therapy comprisesadministering an effective amount of an agent capable of enhancingpositive co-stimulation of T cells.
 55. A method as in claim 54 whereinthe agent is selected from the group consisting of anti-CD40 antibodiesand anti 4-1BB antibodies.
 56. A method as in claim 29 wherein thetherapy comprises administering a cancer vaccine.
 57. A method as inclaim 56 wherein the cancer vaccine is selected from the groupconsisting of dendritic cells loaded with CLL cells or proteins,peptides or RNA derived from dendritic cells loaded with CLL cells,patient-derived heat-shocked proteins, tumor peptides and tumorproteins.
 58. A method as in claim 29 wherein the therapy comprisesadministering an effective amount of an agent capable of activatingreceptors of the innate immune system.
 59. A method as in claim 58wherein the agent is selected from the group consisting of CpG, Luivac,Biostim, Ribominyl, Imudon and Bronchovaxom.
 60. A method as in claim 29wherein the therapy comprises administering an effectiveimmune-enhancing amount of a cytokine.
 61. A method as in claim 60wherein the cytokine is selected from the group consisting of IL-2,GM-CSF and IFN-gamma.
 62. A method for monitoring the progress of atherapeutic treatment, the method comprising: administering animmunomodulatory therapy to a subject; and determining OX-2/CD200 levelsin a subject at least twice to determine the effectiveness of thetherapy.
 63. A method as in claim 62 wherein OX-2/CD200 levels in asubject are determined before administration of the immunomodulatorytherapy and then OX-2/CD200 levels in a subject are determined after atleast one administration of the therapy.
 64. A method as in claim 62further comprising the step of adjusting the dosage amount or frequencyof the immunomodulatory therapy.
 65. A method as in claim 62 whereinOX-2/CD200 levels are determined by detecting a marker that correlateswith OX-2/CD200.